Graft copolymers, methods for grafting hydrophilic chains onto hydrophobic polymers, and articles thereof

ABSTRACT

The present invention relates to synthetic methods for grafting hydrophilic chains onto polymers, particularly hydrophobic polymers such as poly(vinyl chloride) (PVC), poly(vinylidene fluoride) (PVDF), and chlorinated polypropylene (cPP). Resulting polymers include comb polymers which can have a microphase-separated structure of hydrophilic domains provided by the hydrophilic chains. Articles prepared from these comb polymers, particularly derived from PVDF, include membranes for water filtration in which the hydrophilic domains provide a pathway for water transport. PVC can be plasticized by grafting the PVC with hydrophilic chains. In addition, such articles, particularly articles having biomedical applications, can display anti-thrombogenic properties.

RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional PatentApplication Serial No. 60/231,599, filed Sep. 11, 2000.

FIELD OF THE INVENTION

[0002] The present invention relates to new synthetic methods forgrafting hydrophilic chains onto polymers, particularly hydrophobicpolymers. Graft copolymers resulting from these synthetic methods andarticles prepared from these polymers, including membranes and articleshaving plasticizing and anti-thrombogenic properties, are also describedherein.

BACKGROUND OF THE INVENTION

[0003] Commercially available polymers having hydrophilic properties areof great utility, particularly in areas such as such as improvedresistance to the adsorption of oils and proteins, biocompatibility,reduced static charge build-up, and improved wettability to materialssuch as glues, inks, paints and water. Applications for such polymersinclude water filtration membranes and biocompatible medical devices andarticles.

[0004] In many applications, polymers having optimal mechanical, thermaland chemical stability are hydrophobic. Because a hydrophobic polymer orarticle is difficult to wet and is susceptible to fouling, the articlecan be coated with a hydrophilic species, either covalently or byadsorption, or otherwise treated to provide hydrophilic properties.Articles coated in this manner require additional processing steps,which increase the manufacturing cost of the article. Where the articlehas membrane applications, the coating may reduce pore size and thusreduced permeability. In addition, coatings not covalently attached maysuffer from insufficient chemical or mechanical stability. Even if thecoatings are covalently attached coatings, such as those prepared bysurface graft polymerization, residual reactants resulting from thereaction for covalent attachment require extraction prior to use.

[0005] Moreover, surface coverage of graft-polymerized coatings isdifficult to control. Coating of the membrane separation surface doesnot prevent fouling of internal pore channels.

[0006] The development of graft copolymers afforded a possibility toovercome many of the disadvantages discussed above. A “graft copolymer”is produced by covalently bonding a species to be grafted, also referredto as a comonomer, to a parent polymer which provides the backbone inthe graft copolymer. Graft copolymers derived from a parent polymer aretypically used for providing a material with specific properties whileretaining desirable properties of the parent polymer.

[0007] The synthesis of graft copolymers is most commonly accomplishedvia free-radical reactions initiated by exposing the polymer to ionizingradiation and/or a free-radical initiator in the presence of thecomonomer. Free radical syntheses in this manner, however, can be anuncontrolled process. Numerous radicals are present not only on thepolymer but also on the comonomer, which can undergo free-radicalhomopolymerization, resulting in a mixture of homopolymers and graftcopolymers. Thus, a significant disadvantage of these free-radicaltechniques is that the product is typically a mixture of graft copolymerand homopolymer. Moreover, polymer backbone degradation and/orcrosslinking can occur as a result of uncontrolled free-radicalproduction.

[0008] Thus, there exists a need to prepare graft copolymers via afacile, inexpensive process.

SUMMARY OF THE INVENTION

[0009] One aspect of the present invention provides a method comprisingthe steps of providing a catalyst comprising a transition metal halidecoordinated to at least one ligand, and initiating, via the catalyst, areaction between a vinyl group and a parent polymer comprising a repeatunit including a secondary halogen atom.

[0010] Another aspect of the invention provides an article comprising amicrophase-separated comb polymer having a backbone repeat unitincluding a secondary carbon atom. A plurality of the secondary carbonatoms in the polymer are directly bonded to a hydrophilic side chain andthe polymer has hydrophilic domains provided by the side chains.

[0011] Another aspect of the present invention provides an articlecomprising a comb polymer having a hydrophobic backbone in which abackbone repeat unit comprises a secondary carbon atom directly bondedto a halogen atom. A plurality of hydrophilic side chains are bonded tosecondary carbon atoms to the backbone. The comb polymer backbone has amolecular weight no smaller than a molecular weight of the backbone of acorresponding parent polymer.

[0012] Another aspect of the present invention provides a membrane forwater filtration. The membrane comprises a microphase-separated polymerincluding hydrophilic domains having a mean diameter of less than about3 nm, in which the hydrophilic domains provide transport pathways forwater.

[0013] Another aspect of the present invention provides a membrane forwater filtration comprising a microphase-separated polymer includinghydrophilic domains. The membrane is self-supporting.

[0014] Another aspect of the present invention provides a method forwater filtration. The method comprises the steps of providing a membranecomprising a microphase-separated polymer including hydrophilic domains,and allowing water to pass completely through the membrane via thehydrophilic domains.

[0015] Another aspect of the present invention provides an articlecomprising a graft copolymer having a hydrophobic backbone. A backbonerepeat unit comprises a secondary carbon atom directly bonded to ahalogen atom. The article also comprises a plurality of hydrophilic sidechains bonded to the secondary carbon atoms of the backbone. The combpolymer backbone has a molecular weight no smaller than a molecularweight of the backbone of a corresponding parent polymer. The article isresistant to cell and protein adsorption such that the article absorbsless than 90% of protein absorbed by a corresponding parent polymer. Inanother embodiment the plurality of side chains comprises a plasticizersuch that a glass transition temperature of the comb polymer is at least5° C. less than that of a corresponding parent polymer. In yet anotherembodiment, the article further comprises cell-binding ligands attachedto between 1 and 100% of the hydrophilic side chains of the graftcopolymer.

[0016] Another aspect of the present invention provides an articlecomprising a graft copolymer. The graft copolymer comprises a backbonecomprising a polysulfone or polycarbonate derivative. The articlefurther comprises hydrophilic side chains directly bonded tooxyphenylene units of the backbone. The graft copolymer backbone has amolecular weight no smaller than a molecular weight of a correspondingparent polymer backbone.

[0017] Other advantages, novel features, and objects of the inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings,which are schematic and which are not intended to be drawn to scale. Inthe figures, each identical or nearly identical component that isillustrated in various figures is represented by a single numeral. Forpurposes of clarity, not every component is labeled in every figure, noris every component of each embodiment of the invention shown whereillustration is not necessary to allow those of ordinary skill in theart to understand the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 shows a general scheme for preparing grafted copolymers viaATRP according to the present invention, involving addition of a vinylmonomer to a polymer repeat unit denoted as “[R—X]”, in which atransition metal halide catalyst is denoted as M^(+z)X_(n) and acoordinating ligand is denoted as “L_(m)”;

[0019]FIG. 2 shows a scheme for synthesis of PVDF-g-POEM via ATRP;

[0020]FIG. 3 shows ¹H NMR spectra for (a) PVC and (b) PVC-g-POEM^(b) andchemical structure, in which resonances labeled S_(n) are solvent peaksdue to deuterated nitrobenzene;

[0021]FIG. 4 shows ¹H NMR spectra for (a) PVDF_(250K), and (b)PVDF-g-POEM₉ in which resonances labeled S_(n) are solvent peaks due todeuterated DMF, resonances labeled ht and hh are due to head-to-tail andhead-to-head PVDF repeat units, respectively; one or both of thefluorine atoms on each PVDF repeat unit may act as an initiation pointfor monomer addition (b, inset chemical structure);

[0022]FIG. 5 shows GPC traces of (a) PVDF_(250K), the parent polymer for(b) PVDF-g-POEM^(b); trace (c), offset for clarity, is PVDF-g-POEM^(b)following a subsequent 48-h extraction in a large volume of water; themolecular weight scale was calibrated using PMMA standards;

[0023]FIG. 6 shows differential scanning calorimetry (DSC) traces forPVDF, PVDF-g-POEM^(b), and PVDF-g-PMAA;

[0024]FIG. 7 shows a TEM image of PVDF-g-POEM stained with rutheniumtetroxide;

[0025]FIG. 8 shows ¹H NMR spectra for (a) PVDF_(250K), (b) PVDF-g-PtBMA,and (c) PVDF-g-PMAA in which resonances S_(n) are solvent peaks due todeuterated DMF; quantitative hydrolysis of PtBMA to PMAA is confirmed bythe disappearance in (c) of the t-butyl peak b and the appearance of theacid proton peak e;

[0026]FIG. 9 shows gel permeation chromatography (GPC) traces of (a)PVDF _(250K), parent polymer of (b) PVDF-g-PMAA; the molecular weightscale was calibrated using PMMA standards;

[0027]FIG. 10 shows surface atomic percent nitrogen as a function ofgraft copolymer content detected by XPS on the surfaces of as-castPVC-based films (closed symbols) and PVDF-based membranes (open symbols)for samples incubated in 10.0 g/L bovine serum albumin solution for 24 hat 20° C.;

[0028]FIG. 11 shows morphologies of cells incubated for 24 h on as-castfilms composed of (a) pure PVC, (b) PVC plus 10 wt % PVC-g-POEM^(b) ,and (c) pure PVC-g-POEM^(b), and on autoclaved films composed of (d)pure PVC, (e) PVC plus 10 wt % PVC-g-POEM^(b) , and (f) purePVC-g-POEM^(b) ; autoclaving was done for 6 h at 121° C., with thesamples immersed in deionized water; spread or spreading cells areindicated with arrows; magnification is 10×;

[0029]FIG. 12 shows high-resolution C 1s XPS spectra for pure PVC filmsin the (a) as-cast condition, and (b) after autoclaving for 6 h at 121°C. while immersed in water;

[0030]FIG. 13 shows fitted C 1s envelopes for (a) pure PVDF membrane,(b) evaporation cast film of pure PVDF-g-POEM^(b), (c) membranecontaining 5 wt % PVDF-g-POEM^(b), and (d) membrane containing 10 wt %PVDF-g-POEM^(b); for (b), (c), and (d), the computed bulk and surfacecompositions are noted in terms of weight fraction of POEM; for (b), thesurface composition is an average from two samples;

[0031]FIG. 14 shows fitted C 1s envelopes for (a) pure PVDF membrane,(b) evaporation cast film of pure PVDF-g-PMAA, and (c) membranecontaining 10 wt % PVDF-g-PMAA; for (b) and (c), the computed bulk andsurface compositions are noted in terms of weight fraction of PMAA; for(b), the surface composition is an average from two samples;

[0032]FIG. 15 shows pH-dependence of flux through membrane containingPVDF-g-PMAA via a plot of buffer solution flux versus pH for a pure PVDFmembrane and membranes having a bulk composition of 10 wt % PVDF-g-PMAA,after autoclaving for 1 h in water at 121° C.; and

[0033]FIG. 16 shows reversibility of pH-responsive flux of buffersolution through an autoclaved pure PVDF membrane and autoclavedmembranes having a bulk composition of 10 wt % PVDF-g-PMAA, as the pH ofthe feed was alternated between 8 and 2; each half-cycle consisted of a1-min. filtration period for equilibration, followed by a gravimetricflux measurement taken over a second 1-min. period.

DETAILED DESCRIPTION

[0034] The present invention relates to a method for preparing graftcopolymers via a controlled free-radical process. In addition, thepreparation involves a single-step synthetic process. The invention alsoprovides articles comprising graft copolymers, in which a hydrophilicspecies is grafted onto a hydrophobic polymer, thus, providing a methodfor preparing biocompatible biomedical devices. Other graft copolymersdescribed herein are microphase-separated, with hydrophilic domainsprovided by grafted hydrophilic species. Such copolymers can be used toprepare novel membrane materials for water filtration in which thehydrophilic domains provide the primary mode of transport for waterthrough the membrane.

[0035] One aspect of the present invention provides a method for thefacile synthesis of grafted copolymers. “Grafting” involves theprovision of a parent polymer having reactive sites in some or all ofthe repeat units, and adding a species to be grafted (also known as acomonomer) to the parent polymer at the reactive sites. Graft copolymersderived from a parent polymer allow generation of a material withspecific properties while retaining desirable properties of the parentpolymer.

[0036] The present invention advantageously provides a grafting reactionwhich can be carried out in one synthetic step while essentiallyeliminating the formation of undesired species such as homopolymers andchain degradation products, which can result from uncontrolledfree-radical reactions. In one embodiment, the method involves areaction known as an atom transfer radical polymerization (ATRP), whichis a “controlled” free-radical polymerization. This reaction iscontrolled because free radical concentration is kept low and mainlycentered on the parent polymer, preventing the occurrence of numerousundesired reactions. Evidence for eliminating homopolymer formation isnoted, for example, in the molecular weight discussions or Example 1.

[0037] Although ATRP techniques have been previously used for preparinggrafted copolymers, it was commonly believed that the parent polymerrequired very reactive groups to serve as the reactive sites. For manypolymers, direct reaction of a vinyl group with a halogen atom, such aschlorine or fluorine bonded to a secondary carbon atom has not beenfeasible. Thus, previous ATRP reactions for grafting involved the extrastep of substituting secondary halogen atoms with more reactive groups,such as a chloroacetate group. For example, Paik et al. (MacromoleculesRapid Communications 1998, 19, 47) reported grafting styrene and variousmethyl methacrylate side chains onto a polyvinyl chloride-basedmacroinitiator, in which the macroinitiator was modified to incorporatereactive chloroacetate groups as reactive sites for ATRP polymerizationof the monomers. Indeed, Paik et al. stated that “the secondary chlorineon the PVC backbone is too strongly bonded to initiate thepolymerization by reaction with Cu(I) complex.”

[0038] Advantageously, the method of the present invention involvesproviding a catalyst comprising a transition metal halide coordinated toat least one ligand. The method further involves initiating, via thecatalyst, a reaction between a vinyl group and a parent polymercomprising a repeat unit including a secondary halogen atom (i.e. ahalogen atom bonded to a secondary carbon atom). In one embodiment, therepeat unit includes the polymer backbone. “Backbone” refers to thelongest continuous bond pathway of a polymer. In this embodiment, therepeat unit includes a secondary carbon atom situated in the backbone inwhich the secondary carbon atom is bonded to the halogen atom. Thus, thepresent invention allows the direct use of polymer having secondaryhalogen atoms without the extra step of substituting the halogen atomswith more reactive leaving groups.

[0039]FIG. 1 shows a general scheme for preparing grafted copolymers viaATRP according to the present invention, outliningactivation-propagation-deactivation processes for addition of a vinylmonomer to a polymer repeat unit denoted as “[R—X]”. “R” is a secondarycarbon atom and X is a halogen atom, i.e. X is a secondary halogen atom.“R” can be bonded to two halogen atoms or to a single halogen atom plusa second species. For clarity, only one R—X bond is shown here. Thevinyl monomer can be bonded to another organic group, R¹. The transitionmetal halide catalyst is denoted as M^(+z)X_(n) and the coordinatingligand is denoted as “L_(m)” where the ligand, L, coordinated to thetransition metal halide can comprise a bi- or multi-dentate ligand (m=1)or one or more monodentate ligands, depending on the particulartransition metal halide. In one embodiment, the ligand comprises atleast one nitrogen-donor atom, and preferably the nitrogen-donor atom iscapable of interacting with the transition metal.

[0040] During the activation step, the R—X bond is activated to yield acarbon-centered radical [R′] and an oxidized metal complex[M^(+(z+1))X_(n+1)]. During the propagation step, the radical may reactwith a vinyl monomer. During the deactivation step, the polymer isconverted to have a dormant, halogen-endcapped chain.

[0041] The advantages of ATRP synthesis with respect to standardfree-radical techniques arise from the fact that the equilibrium betweenthe dormant and activated chain end species strongly favors the dormantspecies. Thus, the overall concentration of free-radicals is controlledand remains very low throughout the polymerization. Termination andchain transfer reactions, which contribute to uncontrolled chainbranching, crosslinking and increased polydispersity in standardfree-radical polymerizations, are much less probable. But becausepolymerization proceeds by a free-radical mechanism, ATRP can be carriedout without the stringent requirements of living ionic polymerizationswith regard to reagent purity.

[0042] The resulting product is a graft copolymer which comprises acomonomer covalently attached to the parent polymer. In one embodiment,the graft copolymer comprises the same backbone as the parent polymer.The graft copolymer differs from the parent polymer in that the graftcopolymer has a plurality of side chains protruding from the backbone atthe reactive sites. If the reactive sites were present in the parent atregular intervals, the graft copolymer can result in side chains spacedat substantially regular intervals. Such graft copolymers resemble acomb and are accordingly termed “comb polymers.” In one embodiment, thecomb polymers are amphiphilic, i.e. one portion of the polymer ishydrophobic while another portion is hydrophilic. Preferably, the graftcopolymers have a Hydrophilic (polar) side chain and a hydrophobic(nonpolar) backbone.

[0043] In one embodiment, the molecular weight of a backbone of thegraft copolymer is no smaller than a molecular weight of a backbone ofthe parent polymer. Because previous graft co-polymers formed byuncontrolled free-radical reactions resulted in chain degradation, theproducts of the degradation have backbones of smaller length (i.e. lowermolecular weight) than the backbone of the parent polymer. The method ofthe present invention is free of such degradation products and typicallythe molecular weight of the backbone of the graft copolymer is at leastequal to that of the parent polymer.

[0044] In one embodiment, the vinyl group is provided as a portion of ahydrophilic chain, i.e. the vinyl group is covalently attached to ahydrophilic species (e.g. R′ of FIG. 1). Thus, the present methodprovides a facile route to link a hydrophilic species directly to apolymer, and particularly for attaching hydrophilic chains tohydrophobic polymers or articles.

[0045] For example, the hydrophilic chain can comprise a poly(ethyleneoxide) (PEO). PEO is well-known for its ability to resist proteinadsorption, which arises from its hydrophilicity, its strong propensityto participate in hydrogen bonds, its large excluded volume, and itsunique coordination with surrounding water molecules in aqueoussolution. Surface-grafted PEO has been used to render ultrafiltrationmembranes resistant to oil and protein fouling. Preferably, the PEO hasat least 5 ethylene oxide units. The method allows small PEO oligomersor higher molecular weight polymers to be added to the parent polymerbackbone. Examples of hydrophilic chain comprising a vinyl groupattached to a PEO is polyoxyethylene methacrylate (POEM), poly(ethyleneglycol) methacrylate, poly(ethylene glycol) methyl ether methacrylate,poly(hydroxyethyl methacrylate), poly(hydroxyethylacrylate), hydrolyzedpoly(t-butyl methacrylate), hydrolyzed poly(t-butyl acrylate),polyacrylamide, poly(N-vinyl pyrrolidone), poly(aminostyrene),poly(methyl sulfonyl ethyl methacrylate), and copolymers comprisingcombinations thereof.

[0046]FIG. 2 shows a scheme for synthesis of PVDF-g-POEM via ATRP. Thesynthesis involves addition of POEM directly (i.e. no interveninglinker) to a parent polymer containing secondary halogen atoms. Eachrepeat unit of poly(vinylidene fluoride) (PVDF) contains two fluorineatoms attached to a secondary carbon atom. Reaction of PVDF with POEM isinitiated by a transition metal halide, CuCl coordinated to a bidentatenitrogen-donor ligand, bipyridine (bpy). Extraction of a fluorine atomfrom PVDF results in a radical centered on the secondary carbon, as thetransition metal is oxidized. POEM adds at the reactive carbon site toprovide POEM directly bonded to the secondary carbon atom.

[0047] In FIG. 2, the PVDF polymer grafted with POEM is referred to aspoly(vinylidene fluoride)-g-polyoxyethylene methacrylate (PVDF-g-POEM)and encompasses copolymers where either one or both fluorine atoms on atleast some of the secondary carbon atoms are replaced by POEM. Examplesof other grafted polymers include poly(vinyl chloride)-g-polyoxyethylenemethacrylate (PVC-g-POEM), and chlorinatedpolypropylene-g-polyoxyethylene methacrylate (cPP-g-POEM). Every repeatunit need not necessarily be reacted with a vinyl group. For manyapplications, however, a high density of coverage by the graftedcomonomer is desired.

[0048] Many polymers are produced in high volume commercially and areused in the manufacture of numerous articles due to their mechanical,thermal and chemical stability. These polymers, however are hydrophobicwhich precludes their use in many applications unless a pre-treatmentprocess is carried out. Typically, the pre-treatment involves coatingthe article with a species to render the article compatible for use in aparticular application. Thus, it is a feature of the present inventionthat these polymers can be rendered hydrophilic via the grafting methodsdescribed herein. Other possible parent polymers include poly(vinylchloride), poly(vinylidene chloride), poly(vinyl bromide),poly(vinylidene fluoride), poly(vinylidene chloride)-co-vinyl chloride(“-co-” refers to a copolymer), chlorinated poly(vinyl fluoride),chlorinated poly(vinyl chloride), chlorinated polyethylene, poly(vinylfluoride), poly(tetrafluoroethylene), poly(1,2 difluoroethylene),poly(chlorotrifluoroethylene), and copolymers comprising combinationsthereof, such as poly(vinyl chloride-co-iso butyl vinyl ether),poly(vinyl chloride-co-vinyl acetate), poly(vinylidenechloride-co-acrylonitrile), poly(vinyl chloride-co-vinylacetate-co-maleic acid), poly(vinylidene chloride-co-methyl acrylate),and the like.

[0049] Another aspect of the present invention provides an articlecomprising a microphase-separated comb polymer. The comb polymercomprises a backbone repeat unit including a secondary carbon atom. Aplurality of the secondary carbon atoms in the polymer are directlybonded to a hydrophilic side chain. As mentioned previously, “directlybonded” refers to a bond free of any intervening atoms or groups betweenthe secondary carbon atom of the backbone and the hydrophilic sidechain. “Microphase separated” refers to a phase separation of a firstcomponent (e.g. the backbone of the comb polymer) from a chemicallydissimilar second component (e.g. side chains of the comb polymer). Inthe article of the present invention, hydrophilic domains are providedby the side chains, i.e. the resulting plurality of hydrophilic sidechains can aggregate to form hydrophilic domains interspersed withhydrophobic domains comprising the backbone. Domain sizes are dictatedby side chain dimensions and spacing along the backbone and can bedetermined by one of ordinary skill in the art, provided these valuesare known. In one embodiment, the hydrophilic domains have a meandiameter of less than about 3 nm, preferably less than about 2 nM, andmore preferably less than about 1 nm.

[0050] Examples of comb polymers of the present invention include thegrafted polymers include any such graft copolymers previously describedherein, as derived from the parent polymers and hydrophilic chains aspreviously discussed.

[0051] Another aspect of the invention provides an article comprising acomb polymer having a hydrophobic backbone. A backbone repeat unitcomprises a secondary carbon atom directly bonded to a halogen atom,i.e. the repeat unit includes a secondary halogen atom. The comb polymerfurther comprises a plurality of hydrophilic side chains in which eachside chain is bonded to the secondary carbon atom. In one embodiment, atleast about 5 mol % of the secondary carbon atoms in the comb polymerare bonded to a hydrophilic side chain. Depending on the composition ofthe blend, at least about 10 mol %, 25 mol %, 50 mol %, 75 mol %, 90 mol%, or even substantially all of the secondary carbon atoms are bonded toa hydrophilic side chain.

[0052] The comb polymer backbone has a molecular weight no smaller thanthe molecular weight of a corresponding parent polymer backbone. In oneembodiment, this comb polymer backbone molecular weight can be achievedby any method previously described, preferably via ATRP synthesis on aparent polymer. A screening test to determine if the comb polymer makingup the article is encompassed by the present invention, comprisesdetermining an absolute molecular weight of the polymer (e.g. by lightscattering techniques as known by those of ordinary skill in the art)and subjecting the polymer to NMR methods to determine the overallchemical composition and the chemical nature of the linkage between thehydrophilic side chains bonded to the secondary carbon atom, i.e.whether a direct linkage is present, as known by those of ordinary skillin the art.

[0053] This aspect encompasses any backbone, hydrophilic side chain andgraft copolymers described herein. In one embodiment, the polymer ismicrophase-separated and can have hydrophilic domains comprisingpreviously described compositions and dimensions.

[0054] The present invention also features the discovery that membranesfor water filtration can be prepared from the graft copolymers of theinvention. Water filtration membranes allow water (permeant) topenetrate through the membrane while preventing penetration of desiredtarget (retentate) species. Solutes ranging from bacteria or othermicroorganisms, to proteins to salts and other ionic species can befiltered off.

[0055] Filtration membranes can be categorized into porous and nonporousmembranes. In porous membranes, a transport barrier posed is based ondifferences between sizes of permeant and retentate species. Innonporous membranes, such as those used for reverse osmosis, species areseparated by means of solubility and/or diffusivity in the membranematerial. For nonporous membranes and porous membranes fornanofiltration, poor chemical affinity between the membrane material andthe permeant, i.e., water, may inhibit permeability of the permeant.Hence, hydrophobic polymers having the best mechanical, thermal, andchemical properties are not useful for the fabrication of suchmembranes, since they are non-wettable and thus do not allow water topermeate the membrane. For this reason more hydrophilic polymers, suchas cellulose acetate and polyamide, are used for the preparation ofreverse osmosis and nanofiltration membranes. However, these materialsexhibit comparatively poor thermal and mechanical properties, and areeasily chemically degraded or hydrolyzed in aqueous environments.

[0056] In an attempt to overcome these disadvantages, thin filmcomposite membranes have been prepared in which a hydrophilic coating isapplied to the surface of a hydrophobic porous membrane, which acts as amechanical support. Kim et al. (J. Membrane Sci. 2000, 165, pp. 189-199)prepared surface coatings comprising poly(aminostyrene) via interfacialpolymerization atop a porous polysulfone membrane to obtain membranesuseful for RO applications. Nunes et al. (J. Membrane Sci. 1995, 106,49) solution-coated porous PVDF membranes with a polyether-b-polyamidecopolymer (b=block) to create a nonporous surface coating capable ofretaining solutes as small as 1500 g/mol. However, such thin filmcomposite membranes have the disadvantage that the effective filtrationarea of the membrane separation surface is limited to the surface areacomprising pores in the supporting membrane surface, typically less than10 percent of the total area. Moreover, the application of the coatingentails multiple extra processing steps beyond the preparation of thesupport membrane, adding substantially to the fabrication cost. Finally,the coatings of Nunes et al. were observed to degrade in acidic oralkaline solutions.

[0057] Accordingly, another aspect of the invention provides a membranefor water filtration, comprising a microphase-separated polymerincluding hydrophilic domains of less than about 3 nm, preferably lessthan about 2 nm (e.g. for reverse osmosis applications) and morepreferably less than about 1 nm. A feature of the invention is that thehydrophilic domains provide transport pathways for water due to thechemical affinity for water, which facilitates water transport inpreference to the retentate.

[0058] The present invention provides an advantage over thin filmcomposite membranes in that hydrophilic domains across the membranesurface area participate in the transport of permeant, i.e., water.Ideally, the hydrophilic domains provide all the transport pathways, butin reality the membrane may have pinholes or other defects that allowwater to channel through. In one embodiment, the hydrophilic domainsprovide the primary mode of transport for water, i.e. at least 50% ofthe transport pathways, preferably at least 90% of the transportpathways, more preferably at least 95% of the pathways and morepreferably still at least 99% of the pathways.

[0059] The microphase-separated polymer can be a graft copolymer, andpreferably a comb polymer, prepared by methods described herein. Forexample, the graft copolymer can be prepared by ATRP. If residualquantities of transition metal halide catalyst remain in the graftcopolymer, crosslinking of the hydrophobic domains can be readilyachieved through heat treatment of the finished membrane, providingadditional stability.

[0060] Selectivity of water transport can be effectively controlledthrough the membrane pore morphology and dimensions of the hydrophilicdomain. Optimal hydrophilic domain size for a given filtrationapplication can be achieved by varying side chain length of a combpolymer and/or spacing along the graft copolymer backbone. The presentinvention provides the additional advantage that the entire membrane maybe fabricated with a single-step, conventional immersion precipitationprocess. The membranes of the present invention provide the additionaladvantage of enhanced stability over thin film composites prepared bysolution coating methods.

[0061] In one embodiment, the membrane further comprises hydrophobicdomains which provide mechanical, chemical and thermal stability.

[0062] In one embodiment, the membrane is prepared entirely from themicrophase-separated polymer including hydrophilic domains, i.e. it is“self-supporting” (see discussion of “self-supporting” below). Inanother embodiment, the “self-supporting” membrane can comprise a blendof the microphase-separated polymer and at least one other polymer.Preferably, the other polymer is a hydrophobic polymer, examples ofwhich include poly(vinylidene fluoride) and other suitablefluoropolymers, polysulfone, poly(ether sulfone), poly(aryl sulfone),and the like, and polyolefin derivatives.

[0063] The blend can comprise any percentage of microphase-separatedpolymer, so long as the fabricated membrane has the graft copolymer asthe majority component in the dense surface layer of the membrane. It isa feature of the invention that the graft copolymer may be a majoritycomponent in the dense surface layer of the membrane even when it is aminority component in the porous membrane sublayer, due to thecapability of the amphiphilic copolymer to localize preferentially atthe surface during membrane fabrication by immersion precipitation.

[0064] In one embodiment, the microphase-separated polymer is present inan amount of at least 5% by weight of the blend. It is a feature of theinvention that the microphase-separated polymer can be present in smallamounts to render the desired surface properties due to the capabilityof the blend to surface segregate. Surface segregation of one componentresults from certain thermodynamic driving forces, i.e. if reduction ofinterfacial free energy between the two components more than compensatesfor the loss of combinatorial entropy upon de-mixing and, in the case ofexothermic mixing, the loss of mixing enthalpy. Thus, even if a smallamount of the microphase-separated polymer is present, a significantportion of the polymer can occupy the area near the surface of themembrane. In another embodiment, the microphase-separated polymer ispresent in an amount from 5% to 10% by weight of the blend. This smallpercentage of polymer can have a near surface concentration of at leastabout 20% by weight, more preferably at least about 30%, and even morepreferably at least about 40% by weight.

[0065] Presently, many commercially available water filtration membranescomprise an asymmetric structure with a relatively dense, 0.1 to 1 μmsurface layer overlaying a highly porous sublayer. The separationcharacteristics of the membrane are determined by a pore sizedistribution in the surface layer, while the porous sublayer providesmechanical support. Separation is achieved at the membrane surface whilerelatively high fluxes are allowed through the large pore channels whichcomprise the bulk of the membrane volume. A bydrophilic surface can beprovided on this structure by coating this surface layer with abydrophilic groups. This coating, however, may cause clogging of thepores. In addition, flux rates may decrease as water has to penetratethrough several layers.

[0066] Thus, another aspect of the present invention provides a membranefor water filtration comprising a microphase-separated polymer. Thepolymer includes hydrophilic domains. An advantageous feature of theinvention is that the membrane is “self-supporting”, i.e. the membranedoes not require an additional mechanical support, as discussed in Kimet al. (see above).

[0067] The microphase-separated polymer preferably resists theadsorption of proteins and has sufficient wettability properties, asdescribed previously. Moreover, the polymer has sufficientcharacteristics to convey the desired mechanical properties. In oneembodiment, the membrane can comprise a blend of themicrophase-separated polymer and at least one other polymer. Preferably,the other polymer is a hydrophobic polymer and can include any of thehydrophobic polymers described previously.

[0068] In certain embodiments, any article described herein is resistantto fouling. Fouling can result by the deposition of proteins, cells orother larger biological species such as microorganisms. By the provisionof hydrophilic surface chemistry, the susceptibility to fouling isdecreased significantly. In one embodiment, the article is resistant tocell and protein adsorption such that the article adsorbs less than 90%of protein adsorbed by a corresponding parent polymer, and preferablyless than 50%, 20%, 10% or 5% of the protein adsorbed by thecorresponding parent polymer. Typically, the corresponding parentpolymer is hydrophobic and allows deposition of proteins and cells. Theextent an article is resistant to cell and protein adsorption can bedetermined by XPS. For example, immersing a membrane in a solutioncontaining bovine serum albumin (BSA) will allow detection of nitrogendue to BSA adsorption (see Example 4). The adsorption of biologicalspecies such as cells can be determined by microscopy.

[0069] While these embodiments encompass articles comprising any graftcopolymer previously, the invention can also comprise blends includingthe graft copolymer blended with at least one other polymer. One exampleincludes the graft copolymer poly(vinyl chloride)-g-POEM blended withPVC. This blend can result in enhanced protein and cell resistance atthe surface of the article.

[0070] In one embodiment the present invention provides articlescomprising poly(vinyl chloride) (PVC) resistant to the adsorption ofproteins. PVC is a polymer of great commercial importance for thefabrication of medical devices, including IV and blood bags, infusiontubes, circulation tubes, endotracheal tubes, stomach feeding tubes,wound drainage tubes, catheters, and surgical dressings. Due to itshydrophobic nature, however, PVC is susceptible to the adsorption ofproteins from aqueous solution. In blood contacting applications,protein adsorption results in the activation and aggregation ofplatelets followed by thrombosis, as well as activation of thecomplement system leading to systemic immune response, which can resultin organ dysfunction. In other applications, such as PVC endotrachealtubes, protein deposition can lead to an increased risk of bacterialinfection.

[0071] In certain other embodiments, any comb polymer described hereincomprise a covalently bound plasticizer. In one embodiment, the combpolymer comprises a plurality of side chains, such as any side chaindescribed herein, which comprise a plasticizer such that a glasstransition temperature of the comb polymer is at least 5° C. less thanthat of the corresponding parent polymer. In other embodiments, theglass transition temperature is at least about 10° C., 20° C., 50° C. or100° C. less than that of the corresponding parent polymer. For example,PVC has insufficient mechanical properties for many applications unlessplasticizers are added. Plasticizers also improve processability.Because plasticizers usually comprise small molecule organic compounds,a problem with flexible PVC medical devices, which may be composed of upto 45% additives including plasticizers, is the extraction of smallmolecule plasticizers by blood, digestive fluids, and other media whichcontact them. Aside from potential toxic effects, plasticizer leachingfrom PVC devices with long contact times, such as stomach feeding andwound drainage tubes, can cause device hardening and consequent traumato the patient.

[0072] Another aspect of the present invention provides an articlecomprising a comb polymer comprising a poly(vinyl chloride) backbone andhydrophilic side chains. The hydrophilic side chains can comprise groupsexhibiting protein and cell resistant properties. In a preferredembodiment, the hydrophilic side chains comprise poly(ethylene oxide),in which a specific example of such a side chain is polyoxyethylenemethacrylate. Other examples of hydrophilic side chains includepoly(hydroxyethyl methacrylate), poly(hydroxyethylacrylate),polyacrylamide, poly(N-vinyl pyrrolidone), poly(vinyl alcohol), and thelike, and copolymers comprising any of the above, and the like. Thehydrophilic side chains convey enhanced anti-thrombogenicity, as well asa plasticizing effect. The graft copolymer can easily be processed intothe article of manufacture. Due to the covalent bonding of thehydrophilic side chains to the PVC backbone, they cannot be easilyleached into the biological fluid.

[0073] While the invention encompasses articles substantially made up ofthe graft copolymer of the invention, the invention can also compriseblends including the graft copolymer blended with at least one otherpolymer. One example includes the graft copolymer poly(vinylchloride)-g-POEM blended with PVC. This blend can result in enhancedprotein and cell resistance at the surface of the article.

[0074] In certain other embodiments, any article described herein iscapable of being spontaneously wettable. Wettability is a criticalfeature for a water filtration membrane. If the membrane is incapable ofbeing wetted, water cannot pass through the membrane. Wettability of asurface can be quantified by adding water droplets to the surface andmeasuring a contact angle between a droplet of water and the surface. Ahydrophobic surface, such as pure PVDF, is incapable of wetting, and adroplet of water placed on a pure PVDF membrane assumes a high contactangle, which changes very little over time until the drop finallyevaporates. A wettable surface provides low contact angles, preferablyhaving a value of less than about The capability for “spontaneous”wetting can be determined by measuring the time required for the contactangle of the droplet to reach 0°. A membrane of the present invention ispreferably wetted within a time of no more than about 5 min., preferablyno more than about 3 min and preferably no more than about 1 min.

[0075] Another aspect of the present invention provides articlescomprising graft copolymers, comprising a halogenated, hydrophobicbackbone and hydrophilic side chains, having nonspecificprotein-adsorption and cell resistant properties, and specificcell-signaling capability through attached biological ligands. Suchligands include adhesion peptides, cell-signaling peptides, and growthfactors. In one embodiment, the attached biological ligands are attachedthrough the hydrophilic side chains or side chain ends, directly orindirectly, by covalent bonds. An example of such an article comprises agraft copolymer having a halogenated, hydrophobic backbone andhydrophilic side chains containing reactive —OH groups which serve assites for attachment of biological ligands. Examples of hydrophilic sidechains with reactive —OH groups include poly(ethylene glycolmethacrylate), poly(hydroxyethyl methacrylate), and poly(vinyl alcohol).Examples of biological ligands of the present invention include RGD andother adhesion peptides, EGF, TGF and other growth factors, heparin, andthe like. Hydrophobic backbones of the present invention includepoly(vinylidene fluoride), chlorinated polyethylene, poly(vinylfluoride), poly(tetrafluoroethylene), poly(1,2-difluoroethylene),poly(chlorotrifluoroethylene), halogenated polypropylene, halogenatedpolyethylene, halogenated polysulfone, halogenated poly(ether sulfone),halogenated poly(aryl sulfone), and the like, and copolymers comprisingany of the above.

[0076] The function and advantage of these and other embodiments of thepresent invention will be more fully understood from the examples below.The following examples are intended to illustrate the benefits of thepresent invention, but do not exemplify the full scope of the invention.

EXAMPLE 1

[0077] Synthesis of Graft Copolymers by ATRP with Initiation ViaSecondary Halogen Atoms

[0078] Materials. Poly(vinylidene fluoride) (PVDF) ({overscore (M)}_(n)ca. 107 000 g/mol, {overscore (M)}_(w) ca. 250 000 g/mol), poly(vinylchloride) (PVC) (inherent viscosity 0.51), chlorinated polyethylene(cPE) (40 wt % C1), POEM ({overscore (M)}_(n)=475 g/mol), tert-butylmethacrylate (tBMA), copper(I) chloride (CuCl),4,4′-dimethyl-2,2′-dipyridyl (bpy),1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTA), p-toluenesulfonicacid (TSA), 1-methyl-2-pyrrolidinone (NMP), and N,N-dimethylformamide(DMF) were purchased from Aldrich Chemical Co. (Milwaukee, Wis.).Deuterated solvents were purchased from VWR. All reagents were used asreceived.

[0079] PVC-g-POEM. Synthesis Protocol. In a typical reaction, PVC (5 g)was weighed into a conical flask containing a Teflon stir bar anddissolved in DMF (40 ml). POEM (20 ml), CuCl (0.06 g), and HMTA (0.42 g)were then added to the reaction mixture, after which the conical flaskwas sealed with a rubber septum. Argon gas was bubbled through thereaction mixture for 15 min. while stirring. The reaction vessel wasthen placed immediately into an oil bath preheated to 90° C., and thereaction was allowed to proceed for 24 h. The graft copolymer wasprecipitated into a mixture containing 1 part methanol, 1-2 partspetroleum ether, and a small amount of HCl and recovered by filtration.The polymer was purified by redissolving in NMP and reprecipitating 3times in similar methanol/petroleum ether mixtures. Finally, the polymerwas dried under vacuum overnight at room temperature.

[0080] Characterization. Composition. PVC and its graft copolymers werecharacterized by ¹H nuclear magnetic resonance (NMR) spectroscopy indeuterated nitrobenzene using a Bruker DPX 400 spectrometer. The ¹H NMRspectra for PVC and PVC-g-POEM^(b) appear in FIG. 3. In the PVC-g-POEMspectrum, the POEM resonance c at ˜4.3 ppm is convolved with PVCresonance a. The mole fraction of grafted POEM was therefore estimatedas, $\begin{matrix}{X_{{POEM}{({PVC})}} = \frac{\frac{1}{37}\left( {I_{d} + I_{e} + {\frac{2}{3}I_{e}}} \right)}{{\frac{1}{37}\left( {I_{d} + I_{e} + {\frac{2}{3}I_{e}}} \right)} + I_{({a + c})} - {\frac{2}{3}I_{e}}}} & (1)\end{matrix}$

[0081] where I_(x) is the intensity of resonance x and the relationship,$\begin{matrix}{I_{c} = {\frac{2}{3}I_{e}}} & (2)\end{matrix}$

[0082] was assumed from stoichiometry. The compositions of the graftcopolymers appear in Table 1. TABLE 1 Properties of Parent Polymers andGraft Copolymers Graft Copolymer {overscore (M)}_(n) Contact Angle (°)Polymer Composition (g/mol) θ_(adv) θ_(rec) PVC —  71 700^(†) 90.2 82.3PVC-g-POEM^(a) 19 wt % POEM  88 000^(‡) 73.0 42.9 PVC-g-POEM^(b) 50 wt %POEM 143 200^(‡) 42.6 32.4 PVDF — 107 000^(††) 87.5 75.9 PVDF-g-POEM^(a)44 wt % POEM 189 400^(‡) 65.0 28.5 PVDF-g-POEM^(b) 67 wt % POEM 323200^(‡) 38.8 <5 PVDF-g-PMAA 49 wt % PMAA 211 300^(‡) — — cPE — — 96.984.2 cPE-g-POEM 49 wt % POEM — 26.3 16.5 cPP — 254 200^(†) 96.2 93.7cPP-g-POEM 48 wt % POEM 490 300^(‡) 84.8 41.0 PSf —  26 000^(††) 81.474.5 PSf-g-POEM 50 wt % POEM  30 600^(‡) 72.1*, 53.2*, 52.4* 38.5**

[0083] Molecular Weight. Gel permeation chromatography (GPC) wasperformed on the parent PVC and its PVC-g-POEM products intetrahydrofuran (THF) at 30° C., using polystyrene standards forcalibration. GPC of PVC indicated that it had a polystyrene standardmolecular weight of {overscore (M)}_(n)=71 700 g/mol and {overscore(M)}_(w)=131 500 g/mol. The GPC traces of PVC-g-POEM^(a) andPVC-g-POEM^(b) exhibited monomodal distributions shifted up in molecularweight to {overscore (M)}_(n)=80 900 g/mol, {overscore (M)}=177 000g/mol, and to {overscore (M)}_(n)=105 100 g/mol, {overscore (M)}_(w)=170400 g/mol, respectively. The monomodal nature of the peaks rules out anysignificant homopolymer contaminant. However, the molecular weightsobtained by GPC for the graft copolymer products are not good estimatesof their true molecular weights, due to the difference in hydrodynamicvolumes between linear and branched polymers of equal molecular weight.Thus, the number-average molecular weights of all graft copolymers wereestimated from their compositions as obtained from ¹H NMR, using theformula, $\begin{matrix}{{\overset{\_}{M}}_{n,{graft}} = {{\overset{\_}{M}}_{n,{base}}\left( {1 + {x\frac{M_{o}^{POEM}}{M_{o}^{base}}}} \right)}} & (3)\end{matrix}$

[0084] where {overscore (M)}_(n,base) is the number-average molecularweight of the base polymer, x is the molar ratio of POEM units to basepolymer repeat units in the copolymer as measured by ¹H NMR, and M₀^(POEM) and M₀ ^(base) are the molecular weights of POEM and the basepolymer repeat unit, respectively. The molecular weights of the graftcopolymers so calculated appear in Table 1. Aliquots of the copolymerstaken after the last two precipitations were indistinguishable by bothGPC and NMR.

[0085] PVDF-g-POEM. Synthesis Protocol. In a typical reaction, PVDF (5g), POEM (50 ml), CuCl (0.04 g), and bpy (0.23 g) were co-dissolved inNMP in a conical flask, as above. The reaction vessel was similarlypurged with argon gas, after which the reaction was performed at 90° C.for 19 h. The polymer was recovered and purified by successiveprecipitations in methanol/petroleum ether mixtures, as above, and driedunder vacuum overnight at room temperature.

[0086] Characterization. Composition. PVDF and its POEM-graftedcopolymers were characterized by ¹H NMR in deuterated DMF. The ¹H NMRspectra for PVDF and PVDF-g-POEM^(b) appear in FIG. 4. The PVDF spectrumexhibits two well-known peaks due to head-to-tail (ht) and head-to-head(hh) bonding arrangements. Grafting of POEM to PVDF resulted in theappearance of peaks in the region 3.2-4.3 ppm due to the O—CH_(x)bonding environments in the PEO side chains. The solvent peaks S₂ and S₃were subtracted from the spectra using their known intensities relativeto solvent peak S₁ obtained by analysis of pure deuterated DMF. The molefraction of POEM in the PVDF copolymer was then calculated as,$\begin{matrix}{X_{{POEM}{({PVDF})}} = \frac{\frac{1}{37}\left( {I_{c} + I_{d} + I_{e}} \right)}{{\frac{1}{37}\left( {I_{c} + I_{d} + I_{e}} \right)} + {\frac{1}{2}\left( {I_{a{({ht})}} + I_{a{({hh})}}} \right)}}} & (4)\end{matrix}$

[0087] where I_(x) denotes the intensity of resonance x. Thecompositions of PVDF and its graft copolymers appear in Table 1.

[0088] Molecular Weight. PVDF and PVDF-g-POEM^(b) were characterized byGPC in DMF containing 1% lithium nitrate at 30° C., with the molecularweight scale calibrated using PMMA standards. GPC traces for the twopolymers appear in FIG. 5. The grafting reaction resulted in asignificant molecular weight increase, from a PMMA standard molecularweight of {overscore (M)}_(w)=1 218 300 for PVDF_(250K) to {overscore(M)}_(w)=2 979 900 for PVDF-g-POEM^(b). The molecular weightdistribution of the graft copolymer is bimodal. The GPC trace isvirtually unchanged after a 48-h extraction in a large volume of dW, agood solvent for poly(POEM), indicating that its bimodality is not dueto homopolymerization of POEM (FIG 5 c). Rather, the bimodaldistribution is likely a result of radical-radical coupling of chainsduring polymerization, which has been observed previously in ATRP graftcopolymerizations, and which can result in multi-modal molecular weightdistributions. While such termination reactions are generallyundesirable, it will be shown in Example 3 that they do not compromisethe ability of PVDF-g-POEM to surface segregate during the fabricationof PVDF membranes, providing a highly desirable surface chemistry.

[0089] Due to the differences in chain flexibility between thePVDF-based graft copolymers and linear PMMA standards and differencesbetween the hydrodynamic radii of linear and branched polymers of equalmolecular weight, the PMMA standard molecular weights are not accuratenumerical estimates of the true graft copolymer molecular weights. Moreaccurate estimates of the number-average molecular weights ofPVDF-g-POEM were obtained from the NMR data using Equation 3. Themolecular weights so calculated appear in Table 1.

[0090] Thermal Analysis. Differential scanning calorimetry (DSC)analysis was performed using a Perkin Elmer Pyris 1 calorimeter. Allsamples were preconditioned by holding at 210° C. for 15 min., coolingto 130° C. at 10° C./min., holding at that temperature for 15 min., andcooling to 50° C. at 10° C./min. DSC curves were then obtained byscanning from 50° C. to 230° C. at a heating rate of 10° C./min. DSCcurves for PVDF and PVDF-g-POEM^(b) are shown in FIG. 6. PVDF-g-POEMb issemicrystalline, with a depressed melting point compared to pure PVDF.

[0091] Morphology. The morphology of PVDF-g-POEM^(b) was characterizedby transmission electron microscopy (TEM). A bulk polymer sample wasequilibrated in a vacuum oven at 200° C. for 12 h. It was thencryomicrotomed into 50-nm thick sections at −55° C. using a RMC (Tucson,Ariz.) MT-XL ultramicrotome. The sections were mounted on copper gridsand stained with ruthenium tetroxide for 20 min. at room temperature. Itis well known that ruthenium tetroxide selectively stains the ethermoieties in PEO. TEM images of the sections were obtained using a JEOL200CX microscope. FIG. 7 is one such image, in which the stained PEOappears black. Black domains approximately 10-20 Å in size appearedthroughout the sample. This is roughly the expected size of a single 9EO unit POEM side chain. These results suggest that PVDF-g-POEMmicrophase separates, with individual POEM side chains forminghydrophilic domains in a matrix of hydrophobic PVDF.

[0092] PVDF-g-PMAA. Synthesis Protocol. PVDF (5 g) was dissolved in NMP(40 mL) at 50° C. The mixture was cooled to room temperature, afterwhich tBMA (50 mL), CuCl (0.041 g), and bpy (0.23 g) were added and thereaction vessel was sealed with a rubber septum. Argon gas was bubbledthrough the reaction mixture for 15 min. while stirring. The reactor wasthen placed immediately into an oil bath preheated to 90° C., and thereaction was allowed to proceed for 20 h. The graft copolymer wasprecipitated into a 1:1 water/ethanol mixture. It was then purified byredissolving it in NMP and reprecipitating it in a similar water/ethanolmixture. The graft copolymer, PVDF-g-PtBMA, was recovered by filtrationand dried in a vacuum oven overnight. PVDF-g-PtBMA (5.52 g) was cut intochunks ˜2 mm in size, which were immersed in anhydrous toluene (300 mL).The polymer swelled significantly in the solvent, although it did notdissolve. TSA (31 g) was added to the reactor, after which the reactorwas immediately sealed with a rubber septum and the TSA dissolved byvigorous stirring. Argon gas was then bubbled through the reactionmixture for 15 min., after which the reactor was placed in an oil bathpreheated to 85° C. After 7 h, the reaction mixture was poured intoexcess methanol (a good solvent for TSA). Much of the polymer remainedin the form of “chunks,” although some of it was finely dispersed. Thepolymer was recovered by filtration, redissolved in DMF, precipitated ina mixture containing 4 parts hexane and 1 part ethanol, and againrecovered by filtration. For further purification, the polymer wasstirred overnight in a large volume of THF (in which it swelled but didnot dissolve), and precipitated again in a hexane/ethanol mixture. Thegraft copolymer, PVDF-g-PMAA, was finally dried in a vacuum ovenovernight at room temperature.

[0093] Characterization. Composition. PVDF, PVDF-g-PtBMA, andPVDF-g-PMAA were characterized by ¹H NMR in deuterated DMF. NMR spectrafor the polymers appear in FIG. 8. Grafting of tBMA to PVDF resulted inthe appearance of a peak at 1.5 ppm due to the tert-butyl protons.Despite the heterogeneous nature of the hydrolysis reaction, hydrolysisof the PtBMA side chains to PMAA was quantitative, as indicated by thecomplete disappearance of the tert-butyl peak. The spectrum forPVDF-g-PMAA also contained a resonance at 12.6 ppm due to the carboxylicacid proton. The compositions of both PVDF-g-PtBMA and PVDF-g-PMAA werecalculated from their NMR spectra. In both cases, the solvent resonanceS₃ was subtracted using its known intensity relative to solvent peak S₁established by NMR analysis of pure deuterated DMF. The mole fraction oftBMA in PVDF-g-PtBMA was calculated from FIG. 8b as, $\begin{matrix}{X_{tBMA} = \frac{\frac{I_{b}}{9}}{\frac{I_{b}}{9} + {\frac{1}{2}\left( {I_{a{({ht})}} + I_{a{({hh})}}} \right)}}} & (5)\end{matrix}$

[0094] where I_(x) denotes the intensity of resonance x in FIG. 8. Themole fraction of MAA in PVDF-g-PMAA was similarly calculated from FIG.8c as, $\begin{matrix}{X_{MAA} = \frac{I_{e}}{I_{e} + {\frac{1}{2}\left( {I_{a{({ht})}} + I_{a{({hh})}}} \right)}}} & (6)\end{matrix}$

[0095] The calculated values were X_(tBMA)=0.403 and X_(MAA)=0.438,respectively. The close agreement between the two values provides strongevidence that the hydrolysis reaction was selective and quantitative,and that most of the methacrylic acid units of the hydrolyzed copolymerwere protonated. The PVDF-g-PMAA composition reported in Table 1 wascomputed from an average of the two mole fractions above.

[0096] Molecular Weight. GPC of PVDF-g-PMAA was conducted in DMFcontaining 1% lithium nitrate at 30° C., using PMMA standards. GPCtraces of PVDF and PVDF-g-PMAA appear in FIG. 9, where it can be seenthat the grafting reaction results in a significant molecular weightincrease. Unlike PVDF-g-POEM, the molecular weight distribution ofPVDF-g-PMAA is monomodal, providing evidence of neitherhomopolymerization nor radical-radical coupling reactions. As withPVDF-g-POEM, above, a more accurate estimate of the number-averagemolecular weight of PVDF-g-PMAA was obtained from the NMR data using anequation analogous to Equation 3. The molecular weight so calculated isreported in Table 1.

[0097] Thermal Analysis. DSC measurements were performed on PVDF-g-PMAAas described above for PVDF-g-POEM^(b). DSC curves for pure PVDF andPVDF-g-PMAA appear in FIG. 6. PVDF-g-PMAA is semicrystalline, with amelting point slightly depressed compared to pure PVDF.

[0098] cPE-g-POEM. Synthesis Protocol. cPE (5 g), POEM (50 ml), CuCl(0.04 g), and HMTA (0.23 g) were dissolved in NMP in a conical flask, asabove. The reaction vessel was similarly purged with argon gas, afterwhich the reaction was performed at 90° C. for 24 h. The polymer wasrecovered and purified by successive precipitations inmethanol/petroleum ether mixtures.

[0099] Characterization. cPE and its graft copolymer were characterizedby ¹H NMR in deuterated DMF. The ¹H NMR spectrum for cPE exhibitedmultiplets in the region 0.8-2.3 ppm (C—CH_(x)). Grafting of POEM ontocPE resulted in the appearance of well-defined peaks in the region3.2-4.3 ppm (O—CH_(x)) entirely analogous to those observed for thePOEM-grafted copolymers of PVC and PVDF. After subtraction of thesolvent peaks according to the established by NMR spectrum of puredeuterated DMF, the mole fraction of POEM in cPE-g-POEM was roughlyestimated from the ratio of the total intensities of the O—CH_(x) andC—CH_(x) resonances. The estimated composition so obtained appears inTable 1.

EXAMPLE 2

[0100] Thin Film Coatings

[0101] Materials. Chlorinated polypropylene (cPP) (isotactic, 26 wt %Cl), polysulfone (PSf) ({overscore (M)}_(n) ca. 26 000 g/mol), zincoxide (ZnO), and chloromethyl ether were purchased from Aldrich ChemicalCo. (Milwaukee, Wis.). Chloroform and deuterated solvents were purchasedfrom VWR. (Tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-dimethylchlorosilanewas obtained from Gelest, Inc. (Bristol, Pa.). Cell culture reagentswere purchased from Gibco. All reagents were used as received.

[0102] Synthesis of Additional Graft Copolymers. cPP-g-POEM. SynthesisProtocol. cPP (5 g), POEM (50 ml), CuCl (0.04 g), and HMTA (0.23 g) weredissolved in NMP in a conical flask, as above. The reaction vessel wassimilarly purged with argon gas, after which the reaction was performedat 90° C. for 48 h. The polymer was recovered and purified by successiveprecipitations in methanol/petroleum ether mixtures.

[0103] Characterization. cPP and its graft copolymer were characterizedby ¹H NMR in deuterated benzene. The ¹H NMR spectrum for cPP exhibitedmultiplets in the region 0.8-2.3 ppm (—CH_(x)) and in the region 3.3-4.5(C—CH_(x)Cl). Grafting of POEM onto cPP resulted in the appearance ofwell-defined peaks in the region 3.2-4.3 ppm (O—CH_(x)) entirelyanalogous to those observed for the POEM-grafted copolymers of PVC andPVDF. For cPP-g-POEM, the mole fraction of POEM was roughly estimatedfrom the ratio of the total intensities of the O—CH_(x) and C—CH_(x)resonances. The estimated composition so obtained appears in Table 1.

[0104] PSf-g-POEM. Synthesis Protocol. As-received PSf containingoxyphenylene repeat units was first modified to incorporate pendantchloromethyl groups via electrophilic substitution. A solution of ZnO(1.2 g) in chloromethymethyl ether (12 g) was added drop-by-drop to asolution of PSf (6 g) in chloroform (40 mL). After refluxing for 3-5hours at 40° C., the polymer was recovered and purified by successiveprecipitation in methanol and water. The resulting polymer PSf-CH₂Cl (5g), POEM (50 ml), CuCl (0.04 g), and HMTA (0.23 g) were then dissolvedin NMP in a conical flask, as above. The reaction vessel was similarlypurged with argon gas, after which the reaction was performed at 90° C.for 19 h. The polymer was recovered and purified by successiveprecipitations in methanol/petroleum ether mixtures.

[0105] Characterization. PSf, PSf-CH₂Cl, and PSf-g-POEM werecharacterized by 1H NMR in deuterated chloroform. The ¹H NMR spectrumfor PSf exhibited multiplets in the region 0.8-3.2 ppm (C—CH_(x)) and inthe region 6.8-8.0 (aromatic C—H). Adding chlorine to PSf gives rise tothe peak around 4.5 (C—CH_(x)Cl) in the ¹H NMR spectrum for PSf-CH₂Cl.Grafting of POEM onto PSf-CH₂Cl resulted in the appearance ofwell-defined peaks in the region 3.2-4.3 ppm (O—CH_(x)) entirelyanalogous to those observed for the POEM-grafted copolymers of PVC andPVDF. For PSf-g-POEM, the mole fraction of POEM was roughly estimatedfrom the ratio of the peak intensities of the O—CH_(x) and aromatic C—Hresonances. The estimated composition so obtained appears in Table 1.

[0106] Thin Film Preparation. PVC, PVDF, cPE, cPP, PSf, and theircorresponding POEM-grafted derivatives were separately dissolved inappropriate solvents to obtain solutions composed of 2-3 wt % polymer.In addition, PVC and PVC-g-POEM were codissolved for the preparation ofpolymer blends containing 5, 10, 20, 40, and 60 wt % PVC-g-POEM. Thesolvents used were THF (PVC and cPP and their copolymers), toluene (cPEand its copolymers), chloroform (PSf and its copolymer), and methylethyl ketone (at 80° C., PVDF and its copolymer). Thin films were spincoated at 2000 rpm onto silicon wafers (PVDF, PSf, cPE and cPP) or glasscoverslips (PVC). In order to promote adhesion of PVDF homopolymer tothe silicon oxide surface, it was necessary to surface-modify thesubstrate using a fluorinated chlorosilane,(tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-dimethylchlorosilane. Covalentcoupling of the chlorosilane to the surface was accomplished byimmersion of the substrates in a 2 wt % solution of the chlorosilane inethanol at 30° C. for 10 min., followed by a curing step for 10 min. at110° C. in air. Thin films were held under vacuum overnight to removeall residual solvent. Some of the PVC-based films were autoclaved at121° C. while immersed in deionized water (dW, Millipore Milli-Q, 18.2MΩ cm). This treatment was intended to simulate the repeated autoclavesterilizations to which some PVC medical devices are subjected.

[0107] Thin Film Characterization. Contact Angle Measurements. Advancingand receding contact angle measurements (Advanced Surface Technologies,Inc. VCA2000) were performed on thin films and using dW.

[0108] X-Ray Photoelectron Spectroscopy. XPS was performed on thin filmsto determine their near-surface compositions. XPS was conducted on aSurface Science instruments SSX-100 spectrometer (Mountain View, Calif.)using monochromatic A1 Kα x-rays (hυ=1486.7 eV) with an electron takeoffangle of 45° relative to the sample plane. Survey spectra were run inthe binding energy range 0-1000 eV, followed by high-resolution spectraof the C 1s region. Peak fitting of the C 1s region was conducted with alinearly subtracted background and with each component of the C 1senvelope described by a Gaussian-Lorentzian sum function, as detailed ina previous publication (Hester, J. F.; Banerjee, P.; Mayes, A. M.Macromolecules 1999, 32, 1643).

[0109] Static Protein Adsorption Measurements. To investigate theprotein resistance of blends of PVC and PVC-g-POEM, PVC-based thin filmswere immersed in a solution containing bovine serum albumin (BSAFraction V, Sigma). Films were washed with phosphate-buffered saline(0.01 M PBS pH 7.4) for 1 h, then incubated in PBS containing 10.0 g/lBSA for 24 h at room temperature, and washed for 5 min. in three changesof PBS followed by three changes of dW. Finally, samples were dried in avacuum oven at room temperature. Surface coverage of BSA was quantifiedusing XPS, by detection of nitrogen occurring in BSA. Survey spectrawere run in the binding energy range 0-1000 eV, and the near-surfaceatomic compositions were determined using numerically integrated peakareas and applying standard sensitivity coefficients.

[0110] Cell Culture Experiments. Cell attachment studies were performedto evaluate the biocompatibility of PVC/PVC-g-POEM blends. NR6fibroblasts transfected with wild-type human epidermal growth factorreceptor (WT NR6) were cultured in modified Eagle's medium (MEM-α)supplemented with 7.5% fetal bovine serum, L-glutamine, non-essentialamino acids, sodium pyruvate, penicillin-streptomycin, and gentamycinantibiotic. Cell attachment studies were performed on thin films byplacing the samples in tissue culture polystyrene wells and seeding˜34,000 cells/cm² onto each polymer surface in 1 ml of serum-containinggrowth factor medium. Samples were incubated for 24 h at 37° C., afterwhich the adhesion and morphology of cells were assessed using a ZeissAxiovert 100 phase contrast microscope.

[0111] Contact Angle Measurements on Pure Graft Copolymers. Watercontact angles for the pure parent halogenated polymers and theirPOEM-grafted copolymers appear in Table 1. The standard deviations ofall water contact angles listed in Table 1 were <2°. Both advancing andreceding contact angles measured on films of the pure graft copolymerswere substantially reduced compared to the corresponding parentpolymers. PVDF-g-POEM^(b) was particularly notable, with a recedingcontact angle of ˜0°. The high degree of contact angle hysteresisexhibited by the graft copolymers suggests that substantial surfacereorganization occurs upon contact of these materials with water. Thoughhydrophilic and water-absorbent, none of the graft copolymers werewater-soluble.

[0112] Contact Angle Measurements on PVC-Based Blends. PVC-based blendthin films containing 5-60 wt % PVC-g-POEM^(b) were optically clear,both in the as-cast condition and after autoclaving for 6 h at 121° C.,indicating that no phase separated structures larger than the wavelengthof light exist in these blends. Advancing and receding water contactangles for as-cast PVC-based films containing 0, 5, 10, 20, 40, 60, and100 wt % PVC-g-POEM^(b) are listed in Table 2. The standard deviationsfor all measurements were <2°. Addition of the graft copolymer additivesignificantly reduces both the advancing and receding contact angles.The surface compositions of as-cast blends were estimated based on thecontact angles of the pure components using the equation ofIsraelachvili and Gee (Israelachvili, J. N.; Gee, M. L. Langmuir 1989,5, 288):

(1+cos θ_(eq))²=φ_(PVC)(1+cos θ_(eq,PVC))²+φ_(copolymer)(1+cosθ_(eq,copolymer))²  (7)

[0113] where θ_(eq) is the equilibrium contact angle on the blend, φ_(x)is the near-surface volume fraction of component x, and θ_(eq,x) is theequilibrium contact angle on pure component x. In all cases, θ_(eq) wastaken as the average of θ_(adv) and θ_(rec). The estimated surfacecompositions are reported in Table 2. Equation 7 is expected to provideonly a very rough estimate of the surface composition, particularly fora system with such large contact angle hysteresis. Nevertheless, theresults suggest that preferential surface localization of PVC-g-POEM mayoccur in as-cast spin coated blends with PVC, due to differences betweenthe precipitation rates of the two components from THF solution. TABLE 2Properties of As-Cast PVC/PVC-g-POEM^(b) Films Contact Angle ApparentBulk Composition (°) Surface Composition^(†) (wt % PVC-g-POEM^(b))θ_(adv) θ_(rec) (wt %)  0 90.2 82.3  0  5 80.9 68.6 20 10 74.0 57.2 3920 67.7 45.3 59 40 61.3 38.0 74 60 54.3 36.1 84 100  42.6 32.4 100 

[0114] Protein Adsorption Resistance of PVC-Based Blends. Thenear-surface compositions of as-cast PVC-based films exposed to BSAsolution for 24 h were obtained by integration of the following peaks inthe XPS spectrum: Cl 2p (201 eV), C 1s (285 eV), N 1s (399 eV), and O 1s(531 eV). The near-surface concentration of nitrogen occurring in BSA isplotted as a function of blend composition in FIG. 10. Considerableresistance to BSA adsorption is achieved in blends containing as littleas 10-20 wt % PVC-g-POEM^(b). BSA was not detectable on purePVC-g-POEM^(b) films exposed to BSA solution.

[0115] Cell Resistance of PVC-Based Blends. The morphologies of NR6fibroblast cells cultured for 24 h on PVC-based films are shown in FIG.11. In all cases, cells were observed to be confluent on the tissueculture polystyrene surrounding the samples, indicating no evidence oftoxicity. Cells cultured on pure PVC in the as-cast condition (FIG. 11a)adhere, and many spread or begin to spread (black arrows). On as-castfilms containing between 10 wt % (FIG. 11b) and 100% (FIG. 11c)PVC-g-POEM^(b), very few cells adhere, and those cells found on thesurface are rounded or agglomerated, indicating very weak adhesion.Thus, as little as 10% of the graft copolymer additive results in adramatic enhancement in the bioinertness of the PVC surface.

[0116] On as-cast PVC films autoclaved for 6 h in water at 121° C. (FIG.11d), fibroblasts adhere at a high density and spread strongly,indicating strong attachment. XPS analysis was performed to elucidateany differences in surface chemistry between as-cast and autoclaved purePVC films which might explain the significantly enhanced cell attachmentafter autoclaving. The near-surface atomic compositions of the films,obtained by integration of the C1s, Cl 2p, and O 1s peaks in the XPSsurvey spectra, appear in Table 3. The as-cast film has a Cl/C atomicratio of nearly 0.5, as expected based on the stoichiometry of PVC.Autoclaving results in a marked reduction in the Cl/C ratio, as well asthe appearance of a significant amount of oxygen. TABLE 3 Near-SurfaceCompositions of As-Cast and Autoclaved Pure PVC Films Near-Surface at %Atomic Ratio C Cl O Cl/C As-Cast PVC 66.27 33.73 — 0.51 Autoclaved PVC69.10 20.93 9.97 0.30

[0117] High-resolution scans of the C 1s regions of the XPS spectraappear in FIG. 12. The pure PVC spectrum (FIG. 12a) was fit (±1 eV) withthe two well-known peaks of equal area centered at 285.90 eV (CH₂) and287.00 eV (CHCl), as well as a peak at 285.00 eV corresponding to asmall amount of hydrocarbon contamination. Fitting of the spectrum forautoclaved PVC (FIG. 12b) required an additional peak to account for theobvious shoulder at high binding energy. The best fit was obtained withthe additional peak positioned at 289.24 eV, consistent with thepresence of carboxylic acid, which has been assigned a position of˜289.26 eV using high-resolution equipment. The above results areconsistent with thermal degradation of PVC during autoclaving, resultingin dehydrochlorination and the incorporation of oxygenated groups intothe film surface. Thermal, photo-induced, and radiation-induceddegradation of PVC in the presence of oxygen have been known to resultin the creation of polar hydroperoxy and carboxylic acid groups, whichmight be expected to facilitate cell adhesion.

[0118] Fibroblasts exhibit a much lower affinity for autoclaved filmscontaining 10 wt % PVC-g-POEM^(b) (FIG. 11e). On these films, most cellsappear rounded or agglomerated. An occasional cell (arrow) spreads onthese surfaces. As the concentration of graft copolymer additive inautoclaved films is increased, the density of cells observed on thesurfaces decreases and the occasional spreading is suppressed, such thatno spreading is observed on films composed of 40 to 100% (FIG. 11f)PVC-g-POEM^(b). The fact that PVC blends containing the graft copolymeradditive appear to retain much of their bioinert character afterextensive oxidative degradation is significant, as degradation is apotential issue during routine sterilization of PVC medical devices.

EXAMPLE 3

[0119] Membranes

[0120] Materials. PVDF_(534K)({overscore (M)}_(w) ca. 534 000 g/mol),PVDF_(250K)({overscore (M)}_(n) ca. 107 000 g/mol, {overscore (M)}_(w)ca. 250 000 g/mol), and polysulfone (PSf) ({overscore (M)}_(n) ca. 26000 g/mol) were purchased from Aldrich Chemical Co. (Milwaukee, Wis.)and used as received.

[0121] Membrane Preparation. Membranes were prepared from castingsolutions containing polymer(s), glycerol, and N,N-dimethylacetamide(DMAc) according to the compositions listed in Table 4. After filteringand degassing, each solution was cast onto a first-surface opticalmirror (Edmund Scientific Co., Barrington, N.J.) under a casting barhaving an 8-mil gate size. The mirror was then immersed in a bath of dWat 90° C. The membrane was removed from the bath after completeseparation from the mirror and immersed overnight in a second dW bath at20° C. Finally, membranes were dried in air at 20° C. Membranes of typeI, II, and III contained 0, 5, and 10 wt % PVDF-g-POEM, respectively.Membranes of type IV and V contained 0 and 10 wt % PVDF-g-PMAA,respectively. TABLE 4 Compositions of Membrane Casting Solutions g / 100g casting solution I II III IV V VI VII PVDF_(534K) 18.0 18.0 18.0 — — —— PVDF_(250K) — — — 18.0 18.0 — — PSf — — — — — 20.0 18.0 PVDF-g-POEM —0.95 2.0 — — — — PVDF-g-PMAA — — — —  2.0 — — PSf-g-POEM — — — — — — 2.0 glycerol  3.3  1.0  1.0 10.0 10.0 — — DMAc 78.7 80.1 79.0 72.0 70.080.0 80.0

[0122] Membrane Characterization. Contact angle measurements, XPSanalysis, and static protein adsorption experiments were performed onmembranes as described above for thin film coatings.

[0123] Near-Surface Compositions of PVDF-Based Blend Membranes.Membranes Containing PVDF-g-POEM. The near-surface compositions of PVDFmembranes containing 5-10 wt % PVDF-g-POEM^(a) and PVDF-g-POEM^(b) , aswell as a thin-film sample of pure PVDF-g-POEM^(b) , were determined byfitting the C 1s regions of their XPS spectra. The pure graft copolymerfilm was prepared by evaporation casting from a 5% solution in DMAc, andits surface composition is expected to represent an equilibriumcomposition due to the slow evaporation time. The peak centers of thecomponent peaks, referenced to the hydrocarbon peak at 285.0 eV, wereconstrained (±1 eV) as follows: C—COO, 285.72 eV; CH₂ (PVDF), 286.44 eV;C—O, 281.50 eV; COO, 289.03 eV; and CF₂, 290.90 eV. These valuescorrespond to values obtained from pure PVDF, PMMA, and PEO homopolymersusing high-resolution instrumentation. The areas of the CH₂ and CF₂peaks of the PVDF component were constrained to be equal as required bystoichiometry, as were the C—COO and COO peaks of the methacrylateenvironment. The ratio of the C—O and COO peak areas was constrained toits stoichiometric value of 18. For all membranes, XPS analysis wasconducted on the side of the membrane facing the water bath during theprecipitation step of fabrication. In membrane separations, it is thisside of the membrane which contacts the feed solution. TABLE 5 C 1sComponent Peak Areas as Percentages of Total Area for PurePVDF-g-POEM^(b) and for Membranes Containing PVDF-g-POEM CH₂ C—O SampleHC C—COO (PVDF) (PEO) COO CF₂ Membrane, Pure PVDF 3.77 — 48.12 — — 48.12Membrane, 10 wt % PVDF-g-POEM^(a) 5.52 1.57 31.52 28.29 1.57 31.52Membrane, 5 wt % PVDF-g-POEM^(b) 7.42 2.26 23.60 40.86 2.26 23.60Membrane, 10 wt % PVDF-g-POEM^(b) 8.64 3.23 13.31 58.27 3.23 13.31 PurePVDF-g-POEM^(b) 11.48 3.30 11.19 59.54 3.30 11.19

[0124] Component peak area percentages for the membranes and for purePVDF-g-POEM^(b) are listed in Table 5. Plots of the fitted C 1s spectrafor membranes containing 0, 5, and 10 wt % PVDF-g-POEM^(b) appear inFIG. 13. The near-surface mole fraction of POEM was calculated using theformula, $\begin{matrix}{X_{s}^{POEM} = \frac{A_{COO}}{A_{COO} + A_{{CF}_{2}}}} & (8)\end{matrix}$

[0125] where A_(COO) and A_(CF) ₂ are the areas of the fitted COO andCF₂ peaks, respectively. The near-surface POEM contents, converted toweight percent, are listed in Table 6, along with the bulk POEMcontents. Clearly, significant surface segregation of the amphiphilicgraft copolymer in PVDF occurs during the single-step fabrication of themembranes by immersion precipitation, due to the relatively lowinterfacial energy between the amphiphilic component and water. Thus,for membranes containing 5 and 10 wt % PVDF-g-POEM^(b), the graftcopolymer additive is the major component of the ˜60-Å thicknear-surface region of the membrane analyzed by XPS, even though it isthe minor component of the membrane as a whole. TABLE 6 Properties ofPVDF-Based Membranes Comonomer Content Casting (wt %) Solution TypeMembrane Composition Bulk Surface θ_(adv.) initial Wetting Behavior IPure PVDF 0 0 89.9 ± 4.1 nonwetting III 10 wt % PVDF-g-POEM^(a) 4.4 2776.5 ± 3.7 partial wetting^(†) II  5 wt % PVDF-g-POEM^(b) 3.4 42 60.4 ±2.3 wetting, 147 ± 83 s^(‡) III 10 wt % PVDF-g-POEM^(b) 6.7 64 53.5 ±7.0 wetting, 16 ± 10 s^(‡) V 10 wt % PVDF-g-PMAA 4.9 29 75.6 ± 1.0partial wetting^(†)

[0126] Membranes Containing PVDF-g-PMAA. The C 1s regions of the XPSspectra for membranes containing PVDF-g-PMAA were fit with fivecomponent peaks. The peak centers, referenced to the hydrocarbon peak at285.0 eV, were constrained (±1 eV) as follows: C—COOH, 285.80 eV; CH₂(PVDF), 286.44 eV; COOH, 289.33 eV; and CF₂, 290.90 eV, according topreviously determined peak positions for PVDF and PMAA homopolymers. Theareas of the CH₂ and CF₂ peaks of PVDF were constrained to be equal, aswere the areas of the C—COOH and COOH peaks. FIG. 14 shows fitted C 1senvelopes for (a) a pure PVDF membrane, (b) a pure PVDF-g-PMAA filmevaporation cast from DMAc, and (c) an as-cast membrane with a bulkcomposition of 10 wt % PVDF-g-PMAA. Component peak area percentages forthe samples are listed in Table 7. The near-surface mole fraction ofPMAA was calculated from the XPS fits as, $\begin{matrix}{n_{s}^{PMAA} = {\frac{A_{\underset{\_}{C}{OOH}}}{A_{\underset{\_}{C}{H_{2}{({PVDF})}}} + A_{\underset{\_}{C}{OOH}}}.}} & (9)\end{matrix}$

[0127] Bulk and near-surface compositions for each sample appear in FIG.14. TABLE 7 C 1s Component Peak Areas as Percentages of Total Area forPure PVDF-g-PMAA and for Membrane Containing PVDF-g-PMAA C— CH₂ SampleHC COOH (PVDF) COOH CF₂ Pure PVDF-g-PMAA film 21.83 5.41 33.68 5.4133.68 10 wt % PVDF-g-PMAA 28.74 9.19 26.44 9.19 26.44 Membrane

[0128] The near-surface concentration of PMAA in the pure comb films,which were evaporation cast under the same slow conditions used in thepreparation of the PVDF-g-POEM films, was significantly lower than itsbulk concentration as measured by ¹H NMR. This result suggests that PMAAis grafted onto PVDF in the form of long side chains capable of strongorientation away from the air surface to maximize exposure of thelow-energy fluorinated backbone. The near-surface composition of theas-cast membrane (c) indicates substantial surface localization ofPVDF-g-PMAA as well as surface expression of PMAA, such that thenear-surface PMAA concentration is over 6 times the bulk concentration.

[0129] Near-Surface Compositions of PSf-Based Blend Membranes ContainingPSF-g-POEM. The near-surface compositions of pure PSf membranes and PSfmembranes containing 10 wt % PSf-g-POEM were determined by fitting the C1s regions of their XPS spectra. The peak centers of the componentpeaks, referenced to the hydrocarbon peak at 285.0 eV, were constrained(±1 eV) as follows: aromatic C, 284.70 eV; aromatic C—SOO, 285.31 eV;C—COO, 285.72 eV; aromatic C—O, 286.34 eV; CH₂—O (PEO), 286.45 eV; andCOO, 289.03 eV. These values correspond to values obtained from pure PSfand PEO homopolymers using high-resolution instrumentation. The areas ofthe aromatic C—SOO and aromatic C—O peaks of the PSf component wereconstrained to be equal as required by stoichiometry, as were the C—COOand COO peaks of the methacrylate environment. TABLE 8 C 1s ComponentPeak Areas as Percentages of Total Area for Membranes ContainingPSf-g-POEM Aromatic Aromatic C— Aromatic CH₂—O Sample C HC C—SOO COO C—O(PEO) COO Membrane, Pure PSf 73.08 11.54 7.69 — 7.69 — — Membrane, 10 wt% PSf-g- 54.81 14.55 5.63 2.49 5.63 14.94 1.95 POEM

[0130] Component peak area percentages for the membranes and for purePVDF-g-POEM^(b) are listed in Table 8. The near-surface mole fraction ofPOEM was calculated using the formula, $\begin{matrix}{X_{s}^{POEM} = \frac{\left( {A_{PEO}/2.96} \right)}{\left( {A_{PEO}/2.96} \right) + \left( {A_{{aromaticC} - O}/2} \right)}} & (10)\end{matrix}$

[0131] where A_(COO) and A_(aromaticC—O) are the areas of the fitted COOand Aromatic C—O peaks, respectively. The near-surface POEM content ofthe blend membrane, converted to weight percent, is 59 wt % compared tothe bulk POEM content of 5 wt %. Clearly, significant surfacesegregation of the amphiphilic graft copolymer in PSf occurs during thesingle-step fabrication of the membranes by immersion precipitation, dueto the relatively low interfacial energy between the amphiphiliccomponent and water. Thus, for membranes containing 10 wt % PSf-g-POEM,the graft copolymer additive is the major component in the ˜60-Å thicknear-surface region of the membrane characterized by XPS, even though itis the minor component in the membrane as a whole.

[0132] Wettability of PVDF-Based Membranes. PVDF membranes modified withamphiphilic graft copolymers of PVDF exhibit enhanced wettablity. Adroplet of water placed on a pure PVDF membrane assumes a high contactangle, which changes very little over time until the drop finallyevaporates. In contrast, a water droplet placed on a membrane containing5-10 wt % PVDF-g-POEM^(b) assumes a moderate initial contact angle(>50°) which decreases to zero over time and ultimately wets through themembrane. This behavior is termed spontaneous wetting. Herein, thewettability of a membrane was assessed based on the initial advancingcontact angle (θ_(adv)) of a 1 μL droplet of dW placed on its surface,as well as the time required for the contact angle of the droplet toreach 0°. These values are reported in Table 6. The delayed wettingbehavior of membranes modified with PVDF-g-POEM^(b) indicates localsurface reorganization to express POEM upon contact with water.

[0133] Most notable for their wetting behavior are membranes preparedfrom blends containing PVDF-g-POEM^(b). A membrane containing only 5 wt% of this additive (corresponding to a bulk POEM concentration of only3.4 wt %) is spontaneously wettable on a time scale of 2-3 minutes. Thetime needed for complete wetting can be reduced to just a few secondswith the incorporation of 10 wt % PVDF-g-POEM^(b). Membranes containing10 wt % PVDF-g-POEM^(a) (which has a lower POEM content thanPVDF-g-POEM^(b)) or PVDF-g-PMAA do not spontaneously wet. When immersedin water for several hours, however, some regions of these membranesbecome translucent, indicating partial wetting. Pure PVDF membranes showno such behavior. It is of interest to compare this observation withresults obtained previously from PVDF membranes containing the combadditive P(MMA-r-POEM) (Hester, J. F.; Banerjee, P.; Mayes, A. M.Macromolecules 1999, 32, 1643). This additive had a POEM content of 50wt % (greater than that of PVDF-g-POEM^(a)), and the membranes werefabricated under similar processing conditions. Although PVDF membranescontaining P(MMA-r-POEM) displayed substantially enhanced foulingresistance, they exhibited neither spontaneous nor “partial” wettingbehavior.

[0134] Protein Adsorption Resistance of Membranes ContainingPVDF-g-POEM. The presence of POEM at the membrane surface results insignificant resistance to protein adsorption. The near-surface nitrogencontent of membranes exposed to BSA solution for 24 h was obtained byintegration of the following peaks in the XPS survey spectra: C 1s (285eV), N 1s (399 eV), O 1s (531 eV), and F 1s (685 eV). The near-surfaceconcentration of nitrogen from adsorbed is plotted as a function of bulkblend composition in FIG. 10. Compared to PVC/PVC-g-POEM^(b) blends ofequal graft copolymer content (see above), PVDF membranes containingPVDF-g-POEM^(b) are significantly more protein resistant. This result islikely due to the high degree of surface segregation of PVDF-g-POEMwhich occurs during membrane processing. Indeed, a dramatic reduction inprotein adsorption is achieved with a bulk graft copolymer concentrationof only 5 wt %.

[0135] pH-Dependent Filtration Characteristics of Membranes ContainingPVDF-g-PMAA. Control over pore size at the level of Ångstroms isdifficult during membrane fabrication by immersion precipitation. Evenworse, the separation characteristics of membranes always change withtime during operation due to fouling and pore compaction. Thus, polymermembranes are currently not very effective in applications such as thefractionation of macromolecules (e.g., proteins). To address this issue,recent work has opened an intriguing new avenue of research directedtoward the development of environmentally responsive (ER) membranes.These so-called “intelligent” membranes can adjust their own pore sizesin response to environmental stimuli. Thus, for protein separation, onemight envision the employment of an ER membrane in concert with afeedback loop capable of continuously measuring the size of thepermeating solute and adjusting some feed solution attribute to maintainthe desired separation characteristics.

[0136] The most widely studied ER membranes are prepared by the surfacegraft polymerization of weak polyacid chains onto a support membrane(for example, Ito, et al., Journal of the American Chemical Society1997, 119, 1619-1623). Monomers commonly used in this approach includeacrylic acid and methacrylic acid. The weak acid groups on the graftedchains become negatively charged through the dissociation of a proton,

HA=A⁻+H⁺  (11)

[0137] and the degree of dissociation depends sensitively on the localpH and ionic strength. At high pH, the degree of dissociation is high,and mutual repulsion between neighboring like charges causes the chainsto assume an extended conformation, closing the membrane pores. At lowpH, the chains become essentially neutral and assume a relatively morecollapsed configuration, opening the pores. Thus, the chains provide amechanochemical “pore valve” by which separation characteristics andtrans-membrane flux can be controlled simply through adjustment of thefeed solution pH or ionic strength. This effect is completely reversibleand quite dramatic—the difference in trans-membrane flux between the“open” and “closed” pore conditions can be greater than an order ofmagnitude. ER membranes sensitive to pH and to glucose concentrationhave been evaluated for use as drug delivery capsules, which wouldrelease a drug at appropriate times in response to an environmentalstimulus. Membranes having grafted chains capable of photonically andthermally induced conformational changes have also been fabricated.

[0138] Filtration measurements were performed on membranes containingPVDF-g-PMAA to assess the pH-dependence of their permeability. Membraneswere autoclaved for 1 h in water at 121° C. prior to these experiments.The purpose of this step was to eliminate a small, irreversiblepH-dependence of the flux through as-cast pure PVDF membranes. Thisbehavior may be a result of pH-dependent swelling of amorphous PVDF.Heat treatment of the membranes at 121° C. (>0.7·T_(m)) may facilitatecrystallization of PVDF quenched into the amorphous state duringcoagulation. A 25-mm diameter circular membrane was mounted in an Amicon8010 stirred, dead-end UF cell (Millipore) having an effectivefiltration area of 4.1 cm². Delivery of feed solution to the cell wasprovided by a stainless steel dispensing pressure vessel (Millipore)pressurized by a nitrogen cylinder. To simulate the flow conditions inan actual filtration operation, a stir bar mounted above the membraneworked in conjunction with a speed-adjustable stir plate (VWR) toprovide a constant and measured fluid velocity parallel to the membranesurface. Each membrane was prewet with methanol, then immersed in dW for30 min. before it was loaded into the cell.

[0139] Buffered solutions of pH 2-8 were prepared by the addition ofprepackaged buffer salts (Hydrion™, Aldrich) to dW. After mounting inthe UF cell, the membrane was pre-compacted by filtration of pH 8 bufferat an elevated compaction pressure P_(c) for 60 min., followed byfiltration of pH 8 buffer at the measurement pressure P_(m) for 30 min.The values of P_(c) and P_(m), listed in Table 9, varied based on themembrane type. TABLE 9 Compaction and Measurement Pressures Used in pHResponse Studies P_(c) P_(m) Membrane (psig) (psig) Pure PVDF 70 50 10wt % PVDF-g-PMAA 20 5

[0140] Following pre-compaction, the pressure vessel was emptied, suchthat nitrogen gas was delivered directly to the UF cell. The cell wasthen successively emptied and filled with buffers of various pH, and theflux of each solution was measured gravimetrically at pressure P_(m).Each measurement consisted of a 1-min. equilibration period, followed bya gravimetric flux measurement over a second 1-min. period. To assessthe reversibility of the pH response, the trans-membrane flux was firstmeasured during 10 cycles consisting of a pH 8 measurement followed by apH 2 measurement. Following this test, the pH dependence of thetrans-membrane flux was quantified through successive measurements at pH2-8, in intervals of one pH unit. All of the compaction and filtrationsteps were performed at 20° C. with a stirring speed of 500 rpm.

[0141]FIG. 15 is a plot showing the pH dependence of the flux of buffersolutions through autoclaved membranes having surface-localizedPVDF-g-PMAA. The data points for the blend are averages of data takenfrom three different membranes. The self-organizing membranes exhibit aflux variation of well over an order of magnitude, from a flux of 506.5L/m²h at pH 2 to 29.0 L/m²h at pH 8. An autoclaved pure PVDF membraneexhibits very little flux variation with pH. The solid lines in FIG. 15are best-fit symmetric functions of the form, $\begin{matrix}{J = {C - {D\left\lbrack \frac{B^{x - A} - B^{- {({x - A})}}}{B^{x - A} + B^{- {({x - A})}}} \right\rbrack}}} & (12)\end{matrix}$

[0142] where x is the feed solution pH and A, B, C, and D are fittingparameters. The purpose of this fit was not to suggest a particularfunctional form for the data, but rather to obtain an estimate of theapparent pK_(a), given by the pH at the inflection point (the parameterA). The location of the inflection point at pH ˜4.7 is comparable toresults obtained by other researchers from membranes modified by surfacegraft polymerization of PMAA.

[0143]FIG. 16 shows the flux response of these self-organizing,environmentally responsive membranes as the pH of the feed solution wasalternated between pH 8 and pH 2 over a 40-min. period. Again, the datapoints for the blend are averages of data collected from three separatemembranes. After 1-2 equilibration cycles, during which reorganizationof the membrane surface to express the PMAA side chains of the graftcopolymer additive may have occurred, the flux response is completelyreversible over this time period. Each half-cycle consisted of a 1-min.filtration period for equilibration, followed by a flux measurement overa second 1-min. period. Although no quantitative evaluation of therapidity of the flux response was attempted, the flux was observed tochange substantially within a few seconds following exchange of thefiltration buffers.

[0144] This example demonstrates the utility of PVDF-g-PMAA as a blendcomponent for the fabrication of PVDF membranes, wherein the graftcopolymer enables the preparation of membranes havingenvironmentally-responsive separation characteristics with no extraprocessing steps.

[0145] Those skilled in the art would readily appreciate that allparameters listed herein are meant to be exemplary and that actualparameters will depend upon the specific application for which themethods and apparatus of the present invention are used. It is,therefore, to be understood that the foregoing embodiments are presentedby way of example only and that, within the scope of the appended claimsand equivalents thereto, the invention may be practiced otherwise thanas specifically described.

1. A method comprising: providing a catalyst comprising a transitionmetal halide coordinated to at least one ligand; initiating, via thecatalyst, a reaction between a vinyl group and a parent polymercomprising a repeat unit including a secondary halogen atom.
 2. Themethod of claim 1, wherein the vinyl group is a portion of a hydrophilicchain.
 3. The method of claim 2, wherein the reaction provides a graftcopolymer.
 4. The method of claim 3, wherein the graft copolymerincludes a hydrophilic side chain.
 5. The method of claim 4, wherein thegraft copolymer comprises a comb polymer.
 6. The method of claim 5,wherein the comb polymer comprises a hydrophobic backbone.
 7. The methodof claim 4, wherein the graft copolymer is microphase-separated.
 8. Themethod of claim 7, wherein the graft copolymer includes hydrophilicdomains provided by the hydrophilic side chains.
 9. The method of claim3, wherein the molecular weight of a backbone of the graft copolymer isno smaller than a molecular weight of a backbone of the parent polymer.10. The method of claim 3, wherein products of the reaction areessentially free of homopolymer.
 11. The method of claim 1, wherein theligand comprises at least one nitrogen-donor atom.
 12. The method ofclaim 1, wherein the halogen atom is a fluorine atom.
 13. The method ofclaim 1, wherein the halogen atom is a chlorine atom.
 14. The method ofclaim 1, wherein the halogen atom is a bromine atom.
 15. The method ofclaim 1, wherein the parent polymer is selected from the groupconsisting of poly(vinyl chloride), poly(vinylidene chloride),poly(vinyl bromide), poly(vinylidene fluoride), poly(vinylidenechloride)-co-vinyl chloride, chlorinated poly(vinyl fluoride),chlorinated poly(vinyl chloride), chlorinated polyethylene, poly(vinylfluoride), poly(tetrafluoroethylene), poly(1,2 difluoroethylene),poly(chlorotrifluoroethylene), and copolymers comprising combinationsthereof.
 16. The method of claim 4, wherein the hydrophilic chainfurther comprises poly(ethylene oxide).
 17. The method of claim 16,wherein the hydrophilic chain is selected from the group consisting ofpolyoxyethylene methacrylate, poly(ethylene glycol) methacrylate,poly(ethylene glycol) methyl ether methacrylate, poly(hydroxyethylmethacrylate), poly(hydroxyethylacrylate), hydrolyzed poly(t-butylmethacrylate), hydrolyzed poly(t-butyl acrylate), polyacrylamide,poly(N-vinyl pyrrolidone), poly(aminostyrene), poly(methyl sulfonylethyl methacrylate), and copolymers comprising combinations thereof. 18.The method of claim 17, wherein the graft copolymer is selected from thegroup consisting of poly(vinyl chloride)-g-polyoxyethylene methacrylate,poly(vinylidene fluoride)-g-polyoxyethylene methacrylate and chlorinatedpolypropylene-g-polyoxyethylene methacrylate.
 19. A membrane for waterfiltration, comprising a graft copolymer prepared by the method ofclaim
 1. 20. An article comprising: a microphase-separated comb polymercomprising a backbone repeat unit including a secondary carbon atom, aplurality of the secondary carbon atoms in the polymer being directlybonded to a hydrophilic side chain and the polymer having hydrophilicdomains provided by the side chains.
 21. The article of claim 20, therepeat unit further comprising a halogen atom directly bonded to thesecondary carbon atom.
 22. The article of claim 20, wherein the backboneof the comb polymer has a molecular weight no smaller than the amolecular weight of a parent polymer backbone prior to adding thehydrophilic side chain.
 23. The article of claim 20, wherein thehydrophilic domains have a mean diameter of less than about 2 nm. 24.The article of claim 20, wherein the hydrophilic chain is selected fromthe group consisting of polyoxyethylene methacrylate, poly(ethyleneglycol) methacrylate, poly(ethylene glycol) methyl ether methacrylate,poly(hydroxyethyl methacrylate), poly(hydroxyethylacrylate), hydrolyzedpoly(t-butyl methacrylate), hydrolyzed poly(t-butyl acrylate),polyacrylamide, poly(N-vinyl pyrrolidone), poly(aminostyrene),poly(methyl sulfonyl ethyl methacrylate), and copolymers comprisingcombinations thereof.
 25. The article of claim 20, wherein the combpolymer is selected from the group poly(vinylchloride)-g-polyoxyethylene methacrylate, poly(vinylidenefluoride)-g-polyoxyethylene methacrylate and chlorinatedpolypropylene-g-polyoxyethylene methacrylate.
 26. A membrane for waterfiltration, comprising the polymer of claim
 20. 27. An articlecomprising: a comb polymer having a hydrophobic backbone, the backboneincluding a repeat unit comprising a secondary carbon atom directlybonded to a halogen atom; a plurality of hydrophilic side chains bondedto the secondary carbon atoms of the backbone, wherein the comb polymerbackbone has a molecular weight no smaller than the molecular weight ofa backbone of the corresponding parent polymer.
 28. The article of claim27, wherein the polymer is microphase-separated.
 29. The article ofclaim 28, wherein the polymer comprises hydrophilic domains provided bythe hydrophilic side chains.
 30. The article of claim 29, wherein thehydrophilic domains each have a mean diameter of less than about 3 nm.31. The article of claim 27, wherein the hydrophilic chain is selectedfrom the group consisting of polyoxyethylene methacrylate, poly(ethyleneglycol) methacrylate, poly(ethylene glycol) methyl ether methacrylate,poly(hydroxyethyl methacrylate), poly(hydroxyethylacrylate), hydrolyzedpoly(t-butyl methacrylate), hydrolyzed poly(t-butyl acrylate),polyacrylamide, poly(N-vinyl pyrrolidone), poly(aminostyrene),poly(methyl sulfonyl ethyl methacrylate), and copolymers comprisingcombinations thereof.
 32. The article of claim 31, wherein thecorresponding parent polymer is selected from the group consisting ofpoly(vinyl chloride), poly(vinylidene chloride), poly(vinyl bromide),poly(vinylidene fluoride), poly(vinylidene chloride)-co-vinyl chloride,chlorinated poly(vinyl fluoride), chlorinated poly(vinyl chloride),chlorinated polyethylene, poly(vinyl fluoride),poly(tetrafluoroethylene), poly(1,2 difluoroethylene),poly(chlorotrifluoroethylene), and copolymers comprising combinationsthereof.
 33. The article of claim 27, wherein the article is resistantto cell and protein adsorption such that the article adsorbs less than90% of protein adsorbed by the corresponding parent polymer.
 34. Thearticle of claim 27, wherein the plurality of side chains comprise aplasticizer such that a glass transition temperature of the comb polymeris at least 5° C. less than that of the corresponding parent polymer.35. The article of claim 27, further comprising cell-binding ligandsattached to between 1 and 100% of the hydrophilic side chains of thecomb polymer.
 36. The article of claim 35, wherein the cell-bindingligands are cell-signaling ligands.
 37. The article of claim 35, whereinthe cell-binding ligands are selected from the group consisting ofadhesion peptides, cell-signaling peptides, and growth factors.
 38. Amembrane for water filtration, comprising: a microphase-separatedpolymer including hydrophilic domains having a mean diameter of lessthan about 3 nm, the hydrophilic domains providing transport pathwaysfor water.
 39. The membrane of claim 38, wherein the hydrophilic domainsare provided by hydrophilic side chains bonded to a backbone of thepolymer.
 40. The membrane of claim 39, further comprising hydrophobicdomains provided by the backbone.
 41. The membrane of claim 39, whereineach of the hydrophilic chains comprises poly(ethylene oxide).
 42. Themembrane of claim 39, wherein each of the hydrophilic chains thehydrophilic chain is selected from the group consisting ofpolyoxyethylene methacrylate, poly(ethylene glycol) methacrylate,poly(ethylene glycol) methyl ether methacrylate, poly(hydroxyethylmethacrylate), poly(hydroxyethylacrylate), hydrolyzed poly(t-butylmethacrylate), hydrolyzed poly(t-butyl acrylate), polyacrylamide,poly(N-vinyl pyrrolidone), poly(aminostyrene), poly(methyl sulfonylethyl methacrylate), and copolymers comprising combinations thereof. 43.The membrane of claim 38, wherein the hydrophilic domains provide atleast 90% of the transport pathways for water.
 44. The membrane of claim38, wherein the hydrophilic domains provide at least 95% of thetransport pathways for water.
 45. The membrane of claim 38, wherein themicrophase-separated polymer is selected from the group consisting ofpoly(vinyl chloride)-g-polyoxyethylene methacrylate, poly(vinylidenefluoride)-g-polyoxyethylene methacrylate and chlorinatedpolypropylene-g-polyoxyethylene methacrylate.
 46. The membrane of claim38, wherein the membrane comprises a blend of the microphase-separatedpolymer and at least one other polymer.
 47. The membrane of claim 46,wherein the at least one other polymer is selected from the groupconsisting of poly(vinylidene fluoride), polyethylene, poly(vinylfluoride), poly(tetrafluoroethylene), poly(1,2 difluoroethylene),poly(chlorotrifluoroethylene), polypropylene, halogenated polyethylene,halogenated polypropylene, polysulfone, poly(ether sulfone), poly(arylsulfone), polyacrylonitrile, and copolymers comprising combinationsthereof.
 48. The membrane of claim 46, wherein the microphase-separatedpolymer is present in an amount of at least 5% by weight of the blend.49. The membrane of claim 48, wherein the microphase-separated polymeris present in an amount from 5% to 10% by weight of the blend.
 50. Themembrane of claim 38, wherein the membrane is spontaneously wettable.51. The membrane of claim 38, wherein the membrane is self-supporting.52. A membrane for water filtration, comprising a microphase-separatedpolymer including hydrophilic domains, the membrane beingself-supporting.
 53. The membrane of claim 52, wherein the membrane isfree of a mechanical support layer.
 54. The membrane of claim 52,comprising a blend of the microphase-separated polymer and at least oneother polymer.
 55. The membrane of claim 54, wherein the at least onepolymer is selected from the group consisting of poly(vinyl chloride),poly(vinylidene fluoride) and chlorinated polypropylene.
 56. A methodfor water filtration, comprising: providing a membrane comprising amicrophase-separated polymer including hydrophilic domains; and allowingwater to pass completely through the membrane via the hydrophilicdomains.
 57. The method of claim 56, further comprising preventingtargeted species from passing completely through the membrane.
 58. Themethod of claim 56, wherein the hydrophilic domains have a mean diameterof less than about 2 nm.
 59. The method of claim 56, wherein themicrophase-separated polymer comprises a comb polymer having hydrophilicside chains.
 60. An article comprising: a graft copolymer having ahydrophobic backbone, the backbone including a repeat unit comprising asecondary carbon atom directly bonded to a halogen atom; a plurality ofhydrophilic side chains bonded to the secondary carbon atoms of thebackbone, wherein the graft polymer backbone has a molecular weight nosmaller than the molecular weight of a backbone of a correspondingparent polymer and the article is resistant to cell and proteinadsorption such that the article adsorbs less than 90% of proteinadsorbed by the corresponding parent polymer.
 61. The article of claim60, wherein each hydrophilic side chain of the graft copolymer comprisespoly(ethylene oxide).
 62. The article of claim 61, wherein eachhydrophilic side chain of the graft copolymer is polyoxyethylenemethacrylate.
 63. The article of claim 62, wherein the graft copolymeris poly(vinyl chloride)-g-polyoxyethylene methacrylate.
 64. The articleof claim 60, wherein the graft copolymer has hydrophilic side chainsselected from the group poly(ethylene glycol) methyl ether methacrylate,poly(ethylene glycol) methacrylate, poly(hydroxyethyl methacrylate),poly(hydroxyethylacrylate), polyacrylamide, poly(N-vinyl pyrrolidone),poly(vinyl alcohol), and copolymers comprising combinations thereof. 65.The article of claim 64, wherein the backbone selected from the group ofpoly(vinyl chloride), poly(vinylidene fluoride), chlorinatedpolyethylene, chlorinated polypropylene, poly(vinyl fluoride),poly(tetrafluoroethylene), poly(1,2 difluoroethylene),poly(chlorotrifluoroethylene), halogenated polypropylene, halogenatedpolyethylene and copolymers comprising combinations thereof.
 66. Thearticle of claim 60, wherein the graft copolymer is blended with atleast one other polymer.
 67. The article of claim 66, wherein the graftcopolymer is blended with at least one polymer selected from the groupconsisting of poly(vinyl chloride), poly(vinylidene fluoride),polyethylene, chlorinated polyethylene, poly(vinyl fluoride),poly(tetrafluoroethylene), poly(1,2 difluoroethylene),poly(chlorotrifluoroethylene), polypropylene, chlorinated polypropylene,halogenated polypropylene, halogenated polyethylene, and copolymerscomprising combinations thereof.
 68. An article comprising: a graftcopolymer having a hydrophobic backbone, the backbone including a repeatunit comprising a secondary carbon atom directly bonded to a halogenatom; a plurality of hydrophilic side chains bonded to secondary carbonatoms, wherein the graft polymer backbone has a molecular weight nosmaller than the molecular weight of a corresponding parent polymerbackbone and the plurality of side chains comprising a plasticizer suchthat a glass transition temperature of the comb polymer is at least 5°C. less than that of the corresponding parent polymer.
 69. The articleof claim 68, wherein the hydrophilic side chain of the graft copolymercomprises poly(ethylene oxide).
 70. The article of claim 69, wherein thehydrophilic side chain of the graft copolymer is polyoxyethylenemethacrylate.
 71. The article of claim 70, wherein the graft copolymeris poly(vinyl chloride)-graft-polyoxyethylene methacrylate.
 72. Thearticle of claim 68, wherein the graft copolymer has hydrophilic sidechains selected from the group poly(ethylene glycol) methyl ethermethacrylate, poly(ethylene glycol) methacrylate, poly(hydroxyethylmethacrylate), poly(hydroxyethylacrylate), polyacrylamide, poly(N-vinylpyrrolidone), poly(vinyl alcohol), and copolymers comprisingcombinations thereof.
 73. The article of claim 72, wherein thehydrophobic backbone is selected from the group of poly(vinyl chloride),poly(vinylidene fluoride), chlorinated polyethylene, chlorinatedpolypropylene, poly(vinyl fluoride), poly(tetrafluoroethylene), poly(1,2difluoroethylene), poly(chlorotrifluoroethylene), halogenatedpolypropylene, halogenated polyethylene and copolymers comprisingcombinations thereof.
 74. An article of claim 68, wherein the graftcopolymer is blended with at least one other polymer.
 75. The article ofclaim 74, wherein the graft copolymer is blended with at least onepolymer selected from the group consisting of poly(vinyl chloride),poly(vinylidene fluoride), polyethylene, chlorinated polyethylene,poly(vinyl fluoride), poly(tetrafluoroethylene), poly(1,2difluoroethylene), poly(chlorotrifluoroethylene), polypropylene,chlorinated polypropylene, halogenated polypropylene, halogenatedpolyethylene, and copolymers comprising any of the above.
 76. An articlecomprising: a graft copolymer having a hydrophobic backbone, thebackbone including a repeat unit comprising a secondary carbon atomdirectly bonded to a halogen atom; a plurality of hydrophilic sidechains side chains bonded to secondary carbon atoms of the backbone,wherein the graft polymer backbone has a molecular weight no smallerthan a molecular weight of a corresponding parent polymer backbone; andcell-binding ligands attached to between 1 and 100% of the hydrophilicside chains of the graft copolymer.
 77. The article of claim 76, whereinthe cell-binding ligands comprise cell-signaling ligands.
 78. Thearticle of claim 76, wherein the ligands are selected from the groupconsisting of adhesion peptides, cell-signaling peptides, and growthfactors.
 79. The article of claim 76, wherein the hydrophilic side chainof the graft copolymer comprises poly(ethylene oxide).
 80. The articleof claim 76, wherein the hydrophilic side chain of the graft copolymeris polyoxyethylene methacrylate.
 81. The article of claim 80, whereinthe graft copolymer is poly(vinyl chloride)-graft-polyoxyethylenemethacrylate.
 82. The article of claim 76, wherein the graft copolymerhas hydrophilic side chains selected from the group poly(ethyleneglycol) methyl ether methacrylate, poly(ethylene glycol) methacrylate,poly(hydroxyethyl methacrylate), poly(hydroxyethylacrylate),polyacrylamide, poly(N-vinyl pyrrolidone), poly(vinyl alcohol), andcopolymers comprising combinations thereof.
 83. The article of claim 82,wherein the hydrophobic backbone selected from the group of poly(vinylchloride), poly(vinylidene fluoride), chlorinated polyethylene,chlorinated polypropylene, poly(vinyl fluoride),poly(tetrafluoroethylene), poly(1,2 difluoroethylene),poly(chlorotrifluoroethylene), halogenated polypropylene, halogenatedpolyethylene and copolymers comprising combinations thereof.
 84. Thearticle of claim 76, wherein the graft copolymer is blended with atleast one other polymer.
 85. The article of claim 84, wherein the graftcopolymer is blended with at least one polymer selected from the groupconsisting of poly(vinyl chloride), poly(vinylidene fluoride),polyethylene, chlorinated polyethylene, poly(vinyl fluoride),poly(tetrafluoroethylene), poly(1,2 difluoroethylene),poly(chlorotrifluoroethylene), polypropylene, chlorinated polypropylene,halogenated polypropylene, halogenated polyethylene, and copolymerscomprising combinations thereof.
 86. An article comprising a graftcopolymer comprising: a backbone comprising a polysulfone orpolycarbonate derivative; hydrophilic side chains directly bonded tooxyphenylene units of the backbone and; wherein the graft copolymerbackbone has a molecular weight no smaller than a molecular weight of acorresponding parent polymer backbone.
 87. The article of claim 86,wherein the hydrophilic side chain comprises poly(ethylene oxide). 88.The article of claim 87, wherein the hydrophilic side chain ispolyoxyethylene methacrylate.
 89. The article of claim 88, wherein thegraft copolymer is poly(sulfone)-graft-polyoxyethylene methacrylate. 90.The article of claim 86, wherein the graft copolymer has hydrophilicside chains selected from the group poly(ethylene glycol) methyl ethermethacrylate, poly(ethylene glycol) methacrylate, poly(hydroxyethylmethacrylate), poly(hydroxyethylacrylate), polyacrylamide, poly(N-vinylpyrrolidone), poly(vinyl alcohol), and copolymers comprisingcombinations thereof.
 91. The article of claim 90, wherein the backboneis selected from the group poly(sulfone), methyl bisphenolpoly(sulfone), poly(ether sulfone), poly(aryl sulfone), poly(aryl ethersulfone), poly(phenyl sulfone), poly(carbonate), methyl bisphenolpoly(carbonate), poly(ether carbonate), poly(aryl carbonate), poly(arylether carbonate), poly(phenyl carbonate) and copolymers comprisingcombinations thereof.
 92. The article of claim 86, wherein the articleis resistant to cell and protein adsorption such that the articleadsorbs less than 90% of protein adsorbed by the corresponding parentpolymer.
 93. The article of claim 86, wherein the plurality of sidechains comprise a plasticizer such that a glass transition temperatureof the comb polymer is at least 5° C. less than that of the parentpolysulfone derivative.
 94. The article of claim 86, whereincell-binding ligands are attached to between 1 and 100% of thehydrophilic side chains of the graft copolymer.
 95. The article of claim94, wherein the ligands are selected from the group consisting ofadhesion peptides, cell-signaling peptides, and growth factors.